tl;dr: I find the fit "weird" and they don't hold my diaper well
Typical onesies, specifically XP Medicals BodySuit for comparison: Most onesies have a "plunging crotch", such that the sides of your hips are exposed. They run elastic down the plunge, and for me anyway that works well to pull in on my leg gathers and fully seat my leak guards. I usually have the outer lip of my leg gathers outside the onesie in the crotch. Unfortunately, the fit is somewhat critical, and doesn't react well to your changing fit from standing/laying to sitting. You really have to get a onesie that matches your height properly. Too short and when you stand you'll about get your diaper jammed up on your junk and have zero room for circulation, greatly reducing your diaper's capacity. (same applies for laying down) Too tall and it will sag down below and not really do anything useful. Most of them fit snugly around the waist and chest also. XPMedical refers to them as "body stockings" iirc, and that name is appropriate. The material is about as thick as a tshirt, and is all-white. The snap area in the crotch is heavily padded - I though that might be a bit uncomfortable but it works fine. Snaps work fine as long as you didn't go too short, in which case you'll be popping them when you stand up. The top is a "tank top" design, and combined with the plunging crotch, the bodysuit is NOT very warm. I was hoping to wear just that over my diaper around the house, but it gets a bit chilly in the winter. These work very well to hold a diaper in place, even a heavy wet one.
ABU's diapersuit fits a lot like a tall tshirt with snaps installed at the bottom. The sides are very tall, with only a few inches of plunge downward to the snaps. The leg elastic isn't snug at all (for me, and I have arguably wide thighs from biking) Mine was also very loose around my chest and belly. (I'm somewhat skinny, but with a "geek gut", and it still fit loose, so they are MUCH better fitting than most onesies for the heavier folks) The diapersuit also had a much wider crotch snap area, probably designed to accommodate a wide diaper. I personally think they went a bit overboard here though. It would be okay if it plunged down to wrap around my diaper, but it doesn't - it spans horizontally, so the sides of the crotch do NOT go up to meet the leg gathers, leaving what I find to be a very uncomfortable gap and a weird feeling fit. They end up contacting my inside thighs several inches below my crotch. The elastic in the legs however I think is much better than what the bodystocking uses. There's also a pattern on the material. The pattern isn't just in some places, it extends over 100% of the material, which is nice. The material is fairly thin, thinner than a tshirt - it's about the thickness of a bed sheet. There's no additional padding around the snaps, and there's more snaps, but again this doesn't seem to make any difference. Snap performance is the same for both, they hold well. The top is a standard round cut T top. Overall it feels slightly warmer than the bodysuit, but loses a lot of the advantage of the increased coverage due to the thinner material. It doesn't seem to function to hold my diaper up as it only contacts it in the middle of the crotch, instead of wrapping around it.
So comparing the two, I prefer the bodystocking.
