I don't like that it goes into the barrel. The last thing you need is that breaking off and sticking in the barrel when you draw. No matter what it's made of or how it's sized, things happen. Improperly molded plastic, or that's not mixed correctly, exposed to too much heat, whatever the case may be, only 1 in 10000 or 1 in 1000000 might have a problem, but do you want to be that one? There are other ways to achieve a low bulk holster, though I don't approve of most of them.
Another problem with this one...it only covers one side of the triggerguard. That may be fine most of the time, and with many guns, but the one time it isn't, something or someone gets destroyed. With a Glock, both sides of the triggerguard need to be covered to be completely safe. Other guns can get away with covering half or none, but we can't with Glocks.