I came across this thread and thought I'd share as well, for what it's worth. Like Radar I have also tried the Double Front Compression shirt (Item 997) and Extreme Chest Concealer (Item 988) from Underworks. I got the size small, 32-35. I'm very happy with the Extreme Chest Concealer because it only binds the chest and not the stomach as well. Like Eryk mentioned in the thread link that he posted earlier, the Double Front was too uncomfortable. I like being able to breathe. Plus I don't need my stomach to be bound, just the chest. I find the Extreme Chest binder to be very comfortable - it sort of feels like I'm wearing a sports bra, except obviously my chest is much flatter and my dysphoria is lessened. I can put it on the same way I'd put on a tank top. I don't breathe noticeably differently either in normal conditions or when I'm lifting weights. I haven't tried doing aerobic exercise with it though, because it'd be too hot, especially during the summer. The best part about the binder - no more stupid bra lines showing on my back through my t-shirt! Like Radar said, tank top lines are totally acceptable.
Oh, and by the way, when I measured myself according to Underworks' instructions, I was a 32. Perhaps one reason the binder is comfortable is that I'm at the lower end of the size range (32-35).