Here's the low-down without the advertising fluff and paid influencer sponsorships.

Performance

Dyson’s hard floor cleaner doesn’t have vacuum suction, it relies on a scraper to squeeze debris and dirty water off of the roller brush into a tray. The tray has two layers, the top layer traps the solid debris and the dirty water drips through a mesh cutout into the bottom layer. The WashG1 pumps the dirty water from the bottom layer of the tray up into the dirty water tank. The tray is very shallow and can't hold much debris, if the small mesh cutouts are clogged with debris, the dirty liquid won't be able to drain into the lower layer of the tray. Because the dirty water pump is at the bottom layer, if anything blocks the mesh drainage cutouts you're going to get overflow. That overflow goes back to your roller and the floor... gross. This also means you can't use foaming cleaning solution because the debris tray will overflow. Bissel's cleaning solution was designed for their vacuum mops and are lower foaming, but even that will result in foam all over your floors. As another user suggested, Tineco cleaning solution can be used as that has virtually no foaming at all. If your floors have lots of debris and hair particles, it would be far more efficient to vacuum that up first before using the WashG1 as it'd be faster than lugging the device back and forth from your sink to empty the tray. You can't take just the tray because it will spill dirty water all over your floors, you must take the whole machine to your kitchen/bathroom to empty the tray.

Vacuum mops also use a scraper to squeeze dirty water and debris off the roller, but they create a high pressure suction environment to force more of the dirty water out of the roller. All the dirty water is sucked directly into a tank in which the solids are separated from the liquids. This is far superior to Dyson's method as it removes more dirty liquid from the roller brushes.

The Dyson has single-sided edge cleaning, which means that you have to orient the right side of the machine to the wall. The Narwal has double sided edge cleaning , eliminating the need for awkward contortions. The Tineco has double sided edge cleaning along with front edge cleaning so the roller will literally touch the wall from the front too.

Both the Narwal and Tineco handles can rotate down to a completely flat 180° to clean under furniture. The Dyson is pretty close at ~170° and I don't think that holds it back much.

Convenience

The WashG1 doesn't have suction so the "self-clean" function doesn't work at all, leaving you with a soggy wet roller brush that will get disgustingly moldy. After each use, you'll need to remove and empty the tray, rinsing both the top and bottom layer of the tray as it isn't sealed in any way. You'll also need to remove the roller brush frame, which holds two detachable roller brushes and two fixed auxiliary brushes. The frame can be rinsed while the detachable roller brushes should be washed thoroughly with dishwasher soap, wrung of moisture, and left to dry. You must allow the inner cavity of the detachable roller brushes to dry completely before reinstalling, otherwise you may expose the motors to moisture. Then you take a damp paper towel and wipe down the underside of WashG1 before reinstalling all the parts.

Almost all vacuum mops can self-clean by running itself in the dock, then operating in suction only mode to dry itself. Premium vacuum mops have hot air dryers built into their docking station to fully dry the roller brush. In my opinion, the hot air drying is mandatory for true self-cleaning because leaving the roller brush damp will result in moldy odors that builds up between uses.

Cleaning Procedure Comparison

Build Quality

The WashG1 has disappointing build quality. The pivot locking retention feels stiff and sounds like I'm breaking plastic every time I engage or disengage it. The debris tray is friction fit so you have to forcibly pull it out. The retaining mechanism between the top and bottom layer of the tray has loose tolerances, you don't actually need to press the latch to separate them because the tolerances are so bad. This is the only machine I've ever used that has screw-on lids for the clean water and dirty water tanks. The docking station for the WashG1 is literally just a flimsy plastic tray, no special functions aside from charging. It's a bit annoying to align the device to the docking station because it wasn't designed to guide the device to alignment. With the Tineco or Narwal, it will guide itself to alignment so long as it's generally in the right orientation.

As a product engineer myself, I was thoroughly impressed with the build quality of the Narwal. The tolerances are precise and the design is highly optimized to be ergonomic and functional within minimal geometry. Sort of reminds me of an Apple product. The Tineco is also high quality, it feels substantial and the tolerances are a touch looser than the Narwal, with less dimensional optimization resulting in a slightly bulkier design. Of particular annoyance is that Tineco's motors are REALLY loud, their pumps are loud, their vacuum motor is loud, and their roller motor is loud. Narwal's motors are not only quieter, but the noise they produce is deeper which is more tolerable than the higher pitch noise of the Tineco.

Practical Application

I know a lot of people buy vacuum mops for cleaning up pet messes, that's pretty much why I went down this rabbit hole myself. I wouldn't recommend using these to clean up poop, but some models can be effective for cleaning urine and even vomit.

First the Dyson: This machine is unsuitable for pet messes, it would be faster and more convenient to hand clean your pet's mess with paper towels and a spray bottle. If you were to want to clean a pee-pee accident using the WashG1, you're going to have to disassemble everything for manual cleaning, which takes ~15 minutes as opposed to <5 minutes with some paper towel and cleaning spray. Spot cleaning in general just isn't time/effort efficient with the WashG1 due to the manual labor involved in cleaning the device itself. To make it worth using, you'd want to clean your entire house. I will say that the WashG1 is more effective than a traditional mop+bucket as well as a swiffer mop. With a swiffer style mop, you're really just pushing dirt around. A traditional mop+bucket involves diluting the dirty water into the clean water so the WashG1 is more hygienic than that too. However, the WashG1 is less convenient than either of those options, so this device only makes sense for people with OCD.

Vacuum mops: If you pay for a model with hot air drying, you can very effectively use this for heavy duty hard floor cleaning. If you intend to use it for pet messes, this is the perfect option as you can clean up pee-pee accidents in <1 minute between refilling/emptying the liquid tanks. For most vac mops, you'll get around 4-6 spot cleanings between needing to empty the dirty water tank and refill the clean water tank. If you want to use this to clean pet messes or food debris, you WILL need to use detergent of some kind. Both Tineco and Narwal machines only accept their proprietary detergent. Tineco's detergent is pretty cheap when considering you only use a small capful each time you refill the tank. I like Bissell's detergent best, I feel that it has the best cleaning power and most pleasant smell.

Price & Value Proposition

The Dyson WashG1 costs $700, which means that it competes with premium grade vacuum mops that have all the bells and whistles. In all honesty, even an entry level $250-300 vacuum mop is better than the WashG1 in performance, convenience, and price. This device doesn't make any sense and I would not recommend this machine for anyone. I have returned my WashG1, which by the way was an absolute nightmare of an experience due to the horrendous customer support, but that's another story.

In regards to vacuum mops, I highly recommend purchasing a protection plan or extended warranty through your retailer. I never, ever buy protection plans for anything (even my phone), but it's unavoidable with vacuum mops as they tend to fail. My Narwal S10 failed within 2 months, and my Narwal S20 failed after just one use. While the Narwal is on paper the best vacuum mop on the market, the unreliability makes it difficult to recommend. However, I can see why you'd want to roll the dice on the Narwal considering it is priced lower than all other flagship vacuum mops while outperforming them. If you choose to take that chance, buy through a retailer like Amazon that makes returns easy, and purchase the protection plan. The Tineco seems more reliable, there aren't as many failures and considering Tineco vacuum mops are sold in most major retail stores, I suspect they are more reliable than other manufacturers. I doubt retailers would tolerate high return rates.