Owned this Uniqlo bra for around 3 years all the way back when I never thought about bra sizing. I have also simultaneously used it as a sports bra (bad idea). It's ill-fitting for my size, and unfortunately I have experienced difficulty breathing when using it. It's built well, but only for those of which it will fit perfectly.
I usually don't like bras without underwires because they don't give me a good shape and don't stay put. Uniqlo has worked some sort of bra magic with their wireless bras and even the bra tops, because they have a defined shape and stay in place really well. I think a lot of it has to do with the fact that they use firmer materials on the part of the wings right near the cups. Also, even though the gore on a wireless bra will never lay flat, the wire-shaped channels of this bra actually come a lot closer to my chest than in other wireless bras.
So comfortable I own three of these bras! It fits my extremely shallow/conical bust perfectly. The difference between the cup width and cup depth measurements is just ~0.5" on the XS, so these cups are really shallow but large enough to contain my volume. The band is stretchy and could stand to be a smidgen shorter, but it stays in place just fine. The only con is that the cups peek up above my camisoles from time to time.
Lots of fun colors and prints available, and gives a nice, smooth appearance. My go-to day-to-day bra.
About me: Shallow, tall and narrow-average roots, even vertical fullness, close-set but extremely outer full so I don't look close-set at all.
It's comfortable enough and otherwise a good shape match, but this bra is a jack-of-all-trades that asks for inner fullness I don't have. I could push on the inside edge of the molded cup and hit air for a solid inch.
after wearing for several months, I have a few problems with this bra. the gore doesn't tack, the elastic stretches out extremely quickly, and the cups gape at the top slightly. I believe that the last issue is caused by me being full on bottom though. However with all these issues, this bra is still quite comfortable
Plain but clean and sleek appearance. Extremely soft and comfy materials! The band is absurdly loose, even on the tightest set of hooks. The gore-like area in the front floats nearly a full inch away. This seems to happen a lot for me in wire-less bras. If it somehow sat perfectly flat, I'd get slight quadding, but again this has never happened in a wire-less bra for me. I am pretty full on bottom and quite projected. When I hold or pin the band much tighter, the issue is much less pronounced. I am going to get this bra altered (band taken wayyy in and wing height slightly reduced) because the materials are just so comfy! It will probably never be a great fit, but it may be fine for when I want something comfy and semi-supportive. My measurements were taken based on the cup-like part within the molded underwire-like area.
Edit: I gained weight and now it DEFINITELY does not fit... haha