I haven't seen a shirt that untucked wouldn't conceal my 6" 686 with an optic. I can hit a clay pigeon with it at 80 yards and I'd trust it to drop a Mule Deer at that range. I can also draw it and put 7 rounds in an A zone at 7 yards in less than 3 seconds. Much more important than any feat of modest skill I can claim, I can take it and participate in any kind of single or multi-day handgun training class I've ever heard of, so if my skills aren't what they need to be, it will be a good partner in my effort to improve them.
I have nothing bad to say about minature-size .25's and very small .22's with super short barrels. I do however have some doubts about how well they will work out for training -- if for no other reason than their high probability of rejection by the trainers. Gunsite, Thunder Ranch, ITTS, MAG, Rangemaster, Roger's, and countless other schools won't accept them for practically any of their handgun classes. The only exception might be if they had a special pocket pistol class. You can, of course, source your training by an alternative means or attempt to transfer skills learned on a larger handgun to the mini pistol. For myself, I found that the very small guns always resulted in a performance deficit compared to what I carry, train, practice, and hunt with. Since I've never had a shirt that wouldn't conceal it, I can't think of why I'd carry anything else.
