This may work for some people, but I would not use it.
The shirt might work for me, but they don’t have in 4x. 
I thought the whole point of wearing underwear was concealment. Did I miss something?
I have used the shirts. They are an option when your clothing really presents a concealment challenge. A kydex trigger guard is a must because the elastic retention does not protect the trigger. A button up shirt is also a must to get access to the gun (either get the snaps or plan on popping some buttons). If you use the elastic under both arms you can carry a single stack gun, flash light, spare mag, and a folding knife. Using the second side sort of helps balance the weight of the pistol. If you carry a gun with a grip safety like an XDs or a 1911 type gun you won’t be wanting the elastic retention strap, and can save a lot of money by buying the seconds off of e-bay.
I use the shirts every day. I find no problem with the trigger - it hides beneath the holster.
@Bugleboy - the shirts conceal very well.
I noticed they didn’t have those shorts with “appendix carry” as an option…probably because the picture of that hits a lot closer to home than just seeing an appendix holster on a pair of jeans…
I have one of the men’s shirts… I find the heavy elastic and velcro really annoying on the sensitive inner-arm skin. But it does secure the firearm effectively.
@Zee - Velcro? None of mine have velcro. Mine have metal clips that hold the firearm in place under either arm.
I like the shirts maybe. I don’t think the shorts would be very usable for me. I don’t even carry IWB much.
I almost always have the same comfortable holster.