I like the 5.11 shirts, but the others that you'll find online or at gun shows are different. They put the gun further back and for me it made the gun nearly inaccessible. I'm pretty thick in the chest, which makes it difficult. Compared to a regular vertical shoulder holster, those shirts put the gun an inch or more further back.
As far as belly bands, I have one that I use when I'm in gym clothes. It's comfortable enough to wear all day around the house as well.
My only issue with it is that mine doesn't have a thumb break. That's generally not a problem, it held the gun well, but I was wearing it one day when I went to the doctor. I forgot that this particular doctor pulled my shirt up when listening to my heart & lungs; most of my doctors listen through my shirt. Well, he pulled my shirt up quickly and unexpectedly. My hand didn't get back fast enough and my shirt grabbed the butt of my Walther PPS, yanking it out of the belly band and sending it flying to the floor. Needless to say, the doctor freaked out and I left it in the car or kept it in my pocket after that. He slowed down on pulling my shirt up too.
It did allow me to confirm that the Walther drop safety works...