Having just got hands/face on a pair of I4's on saturday, I gotta say I felt a bit exposed. I have a narrow little face compared to most, and even my jaw was hanging out. I think they make you look like a pigeon too, but that's simply my taste and is irrelevant in discussing the actual quality of the mask. As far as build quality goes, they felt solid and fitted nice and close, but seemed a bit more rigid (nopt hugely, just a bit) than the e-vents I'm used to. I'll add, however, that the rigidity gives them more of a fixed feel on your face, like they won't come off.
In summary: though I think the build quality and fit of the I4's is laudable, I think they're ugly and leave my jaw a bit exposed, and when you play snake you get mugged in the face/neck every now and then making face protection more valuable imo. I'll stick with my e-vents (maybe buy a new pair now the foam is coming off = shoddy build quality) and flex's for now.