I installed Godmorgon in one bathroom and now working on the second one. In my opinion, you need to pay at least triple to get similar quality from someone else. The cabinets have 2 or 4 (depending on the size) fully working deep drawers. But here it gets complicated. The cabinets rely on the cool low profile drain system, that is bundled with the countertop. If you want a different top, you will have to buy the regular drain components, and they will interfere with the drawers. It is possible to modify the drawers, but you will lose storage capacity and it may not look good. As for the countertops themselves, I don't really care for both acrylic and porcelain options. I installed the acrylic, and I can live with it, but the sink is very shallow and it seems like it is getting harder to clean around the faucet. Despite the shortcomings, I would still use IKEA top for compatibility with the vanity. Single hole faucets are plentiful and inexpensive. More on reddit.com

Having bought IKEA for years I'm pretty sure engineered wood quality is the same for both kitchen and bathroom cabinets. More on reddit.com

If you are not planning to use the rear brackets to support the cabinet on a rail or directly into the wall structure, you can certainly cut a 24" deep cabinet shorter to 21" but you'll need a table saw or track saw to cut a new slot for your back board. You could possibly use the cut off portion as a template to guide you. I would recommend that you support your cabinet from underneath on 4 euro-style adjustable feet attached to the bottom of the cabinet. Don't bother with the Ikea Sektion cabinet legs. Alternatively, you could look at the 14 3/4" shallow Sektion base cabinets, and stand them 7" away from the rear wall, but be sure to secure it directly to the floor or support them by attaching them directly to the wall. Unfortunately that may have some consequences for sink depth, and you will only be able to use the shallow Maximera drawers. More on reddit.com

They handle the wet-ish environment of a kitchen, no reason they wouldn't hold up in a bathroom. If you're going to use a 30" or 36" standard cabinet for the sink, and you're able to keep all of the plumbing in the back 1/3 of the cabinet, IKEA makes shallow drawers that can be installed in standard depth cabinets (all of the plumbing would be behind the drawers). You could do drawers on the bottom 2/3 of the cabinet and a dummy panel on the top 1/3 where the sink is. More on reddit.com