I know there aren't a ton of reviews out there, and I have such a strange issue that led me to this point that I'm uncertain this will be helpful for most here. But let's go anyway.
Stats: 4'10", 125 pounds. Extreme pear shape. Hip, back, and neck injuries. Chronic tailbone pain. Cold sleeper. Stomach and side sleeper.
Why I Bought this Topper: The Purple bed I purchased was the first time in a long time I wasn't waking up with pressure point pain But I was waking up with deeper pain. The springs weren't good enough, I was simply sinking too much at the hips, and my lower and upper back were screaming. I loved, loved the gel matrix. The support layer wasn't up to the job of supporting the gel and the sleeper. (The gel weighed roughly 60 pounds, based on the calculation I did.) I had tried adjusting the support by stuffing a towel under the mattress at the hips, but it didn't help. It was possible to firm up the mattress by putting a blanket over the top, under the sheet, but for a twinXl, it was 2600 dollars, and I did not feel compelled to play DIY at that price point. But I liked the feel of the gel.
The Setup: I purchased the Intellibed topper with the idea of purchasing springs for it as well and treating it as a comfort layer in DIY build, but I decided instead to put it on an airbed to start, to see if I could possibly better define just how stiff I want the springs to be. A double height airbed proved impossible to get firm enough. I moved it to a single height, and that's proving much better at providing the desired support. There is no mention that the bed requires knit sheets, like the purple, and I've been using tencel sheets. The pressure relief is very good anyway. I don't think that you need to use knit sheets unless you really want to, and given that I don't like them -- great!
The Topper: My first impression was that it looked and felt cheap. Something about the quilted cover and the straps (yes, it comes with straps to anchor it to the mattress) felt like the 90s. I expected it to be a quilted knit cover, or have a clean, modern look. It does not. The matrix grid is actually under a layer of what I think is high-end poly foam. So 2.25" of gel matrix, maybe 1.5 inch of mystery foam (couldn't tell me what it was, it doesn't feel much like latex) and then a half inch of whatever they use for the quilted cover. Despite appearances, this is actually quite comfortable just on the floor, and for an RV, this could be slung right over one of those ultra-short, ultra firm bed pads to make a pretty darn comfy bed, in my opinion. It's also brutally heavy -- 67 pounds. However, this is a lot better than wrangling an entire effing mattress around.
The Results So Far: The Intellibed gel is much firmer than the purple gel, hence why there is a foam layer over it. This makes the Intellibed topper sleep warmer, and I don't love that for summer, but now that nighttime temps are falling again, I'm thinking this is a little chilly, and I might need to pad up the bed with a fleece blanket under me when it gets to being fall. The topper does soften up a bit once it warms up, so it feels very firm when I get into bed, but in the morning, it's forgiving. I would say it takes maybe half an hour to an hour to come up to temp, as it were. Fortunately or unfortunately, if you get out of bed to go to the bathroom in the night (I do) it doesn't hold heat very well and you'll come back to a distinctly colder bed.
I think the topper also shows to best advantage over a very firm base. The floor is really too firm for me, and I think the topper really is intended to be used on something with a bit of give for longevity. The airbed is pretty firm. Maybe not zoned coils firm, but honestly, not that far off. Much firmer than Purple's coils. It's so firm I have decent edge support.
Who I think this product is for: Given that the word on the street is that this gel product was developed for medical applications, my theory is that I'm weirdly exactly who this was for. Someone who wants that firm, firm, FIRM base, but then needs a lot of pressure relief where they interact with the mattress.
This is for sleepers who want a sense of floating on their mattress. If you like the way memory foam gets out of the way, but find the support sad, and latex just fights back too much, I feel like the gel matrix might be the right fit. If you've often felt like you need stronger springs and wimpier comfort layers to get comfy, but changing the foam around just makes it so you have bad pressure points this product seems to address that sort of sleep challenge.
DIY? I've given this a lot of thought, and while you can buy gel matrix from China, the shipping is crazy, and it just seems risky. However, I have thought that it's possible that 1-2 inches of medium latex over 2.5 inches of firm or extra firm memory foam may very well give a very similar effect. I would say if you try that build, and it's moving in the right direction, but not a winner, that stepping up to trying the Intellibed topper could be a good move towards comfort.