I've never used the full face ones but dislike the design it seems like a solution in search of a problem (which leads to many more problems than you had with the conventional approach). Honestly, other than looking cool, what do they improve? I can see a ton of problems (no way to deal with fog, no way to equalize, horrendous buoyancy, a flood screws up your sight and breathing concurrently, etc.)
I do know people that tried them and loved them though so I will give it a shot when I can borrow one. Really low expectations though.