I wear these T-shirts everyday. I'm a big and tall guy and they stay tucked, hold their shape, and stretch where I need them to. At first I didn't like the collar, but it doesn't lose its shape so I'm all for it now!
I was looking for a shirt that maintained the neck shape and wouldn't "bacon" - as well as an undershirt rode high enough to wear with button-ups and polos without looking like an old rag that I threw on in haste. Been through a few washings now, and it is still looking good. (It has even stood up to my whiskery neck pretty well and isn't yet showing the excessive fuzzing that I see with other Ts). The material is great for form-fitting under your shirts as well - quite comfortable.
I usually wear these t-shirts underneath something else, but they look great either way. They're very comfortable, fit a "big guy" just right. My only concern is with the neck...I think it's tapered too high...can be uncomfortable at times. A v-neck version would be a great alternative!