I had training pants with a hidden PUL layer for my first dd and absolutly hated them! The problem with 'hidden' layers like that (wether they be in diapers or training pants) is that it means that the inner absorbent layers are in direct physical contact with the outer fabric layers. So as soon as the inside gets wet it automatically wicks this wetness to the outside. Honestly unless we're talking about teeny tiny little dribbles, that inner PUL layer is pretty much useless.
So while they will probably work fine for teeny little dribbles, I wouldn't recommend adding absorbency in hopes that they'll work for anything more. The problem won't be the lack of absorbency but the wicking effect from inside to outside. Training pants like this do indeed resemble regular underwear the most, but honestly they don't offer that much more protection either...