So, to start with, I'm not large chested; but I'm not super small chested, either. I'm also a larger guy at 5'11'' and 200lbs - which meant that I learned fast that T-Kingdom (a Taiwanese company) binders were definitely made for MUCH smaller dudes.
For shipping and sizing, Underworks has always been spot on when it comes to shipping stuff fast and also with item returns. Twice now I've ordered a binder and, once received, tried it on to learn that it was either too small or too large. Then I'd put the product back in its packaging, throw the receipt in with my corrections scribbled on it, mail it back and they swiftly send another in the correct size. No question.
Here's my 2 cents on binders I've tried, most excellent to most lame:
Underworks Style 974: Second favorite. It's extremely comfortable and I frequently combine it with the T-Kingdom M801 if I want a particularly flat chest. This is also the binder that I use at the gym. On the downside, because of the cotton outer-portion it can get a bit hot under a shirt. It also doesn't bind too tight, which works with certain shirts and not others.
Underworks Style 988: Not as comfortable as the muscle shirt, but also not uncomfortable. This is the most comfortable binder I've worn so far that binds enough alone without the help of the T-Kingdom M801. The picture above makes it look like the entire thing is tight but, in reality, it only compresses at the top and turns into a light cotton shirt at the bottom. I love this for lighter shirts because it looks just like an undershirt. It's also better for hot days because my stomach/lower-back skin can breathe (unlike the 974, which is snug all over). The only con I've experienced with it so far is that it can cause my lower back to ache a bit after a while, but not always.
Underworks Style 967: Comfortable and would definitely bind smaller-chests enough - but it sucks without a piss-n-packer because it's an entire body suit. Without it, I have to remove my shirt in order to get it pulled down. Another con is that the compression pulls my shoulders forward on this one more than my other binders, so I feel like I'm in a constant struggle to stand up straight.
Underworks Style 918 (Swim Tank): Not long enough for tall guys, but compresses more effectively than any other binder I've tried. I will only wear it for very short periods of time when I want a super flat chest in a tight shirt. I haven't felt comfortable going swimming with it yet, but I suspect I'd rather just float around in the water with it vs. actually doing any swimming because of how compressed I am in it.
T-Kingdom Model 1700: HATED it. It killed my lower-back. The Velcro was a pain in my side to work with. I gave it away to my poor schlub friend, Erin. Hopefully it works for his body type better.
T-Kingdom Model 1980: Really disliked this one. It was really uncomfortable. And it was so short that I had to constantly tuck and re-tuck it into my pants. I considered sewing additional material to it for tucking, but the soft material would've shredded even sooner. And it only last for about 5 months before it fell apart on me. Literally.