(Reviewer of upper mid size chest)
Much the same as the normal Tri-Top, but with a cotton lining. If you have any chafing problems against your skin in the original, I imagine this is better. Or if you just prefer something that feels a bit more clothes-like in general.
2 Layers front and back, the elastic and the cotton. No noticeable difference from the norm and seems just as strong.
In weather where you just want this and no undershirt under your shirt, you could turn it inside out and it would look like a completely ordinary vest.
Seems to hold things in place a bit better for me, but then it is new and your mileage may vary.