Wish I could give 3.5 stars. It does the trick, first shirt I've tried that actually blocked sweat. But it was also really thick and uncomfortable and heavy in the underarms, and completely visible even when buttoning my shirt up all the way because the neck is too high. Also really expensive for an undershirt.
Also, it looks like an undershirt with underarm pads, definitely cannot be worn on its own. So the fact that it also can't be worn under anything is a deal breaker.

All that said, it solves the problem. *if* they release low V necks I'd get more, especially if they were $20 instead of almost $40. As is, can't wear it under most things, so not worth it.