Well, sadly we just returned from 2 weeks at Poly (Club level room, but no Club level services are currently being offered, because pandemic) It was a roll-in shower room in the Hawaii building. I say "sadly" because I could have stayed for another 2 weeks... or more if only real life didn't keep trying to get in the way!
We had the mesh seat in that shower - the room, btw was beautiful, and we faced the quiet pool, on the ground floor, with a "walk through" door instead of a standard sliding door, which was lovely, although it required either a helper to hold it for me, or a manual door stop in place.
The mesh seat is still problematic for me. Aside from the hygiene issue (it's just an *ick* factor for me; I think because I don't know how they are cleaning/sanitizing them - I always put down a towel over the mesh because I cannot bring myself to sit on it without something between me and that seat) it was painful for me to use, (probably because I still have ongoing tailbone/lower back issues) and I did slip halfway off once during a transfer, which resulted in a VERY painful situation that can only be likened to slipping off the seat of your bike, and onto the "sissy" bar...
After that, we kept the built-in seat folded up, and I used my personal folding travel shower seat that we brought, which worked well because I could face it the way I wanted to sit anyway. The worst downside to that was the handheld shower hose was not very long, which limited my placement within the shower.
Otherwise, the shower drained well, and there was a lovely clear silicone rubber seal across the shower door that worked just fine to keep water in the shower. I always forget that the water at WDW is "softer" than our water at home, and so my first shower is always a struggle to get the shampoo out of my hair!
Not sure of how the roll-in showers in that building used to be, (before the most recent remodel) but this one was more similar to the roll-in showers at POFQ or POR, with a 32-inch door opening, and a wall-mounted seat next to the opening that faced the rear wall of the shower.
This shower was smaller than POR or POFQ - I know because I took my "standard" length of non-slip material for the shower floor, and it was too long by several inches... where at POFQ and/or POR, it actually fits the floor with about 1-½ inches to spare on both ends! I thought they were using the "standard" bathtub sized opening for those types of showers, but even my other family members noticed that this shower was smaller in both length and width.