out of the two i prefer the I4's, having owned both.
The grillz fit virtually anyones face, ( unless your about 3 years old ) and offers good hearing and speaking, but i found mine fogging up alot when it was really bad to, like in the middle of a gunfight. They are heavier than the i4's, and the special lenses with the mirror scratch so easily its untrue. One real peeve i had about them was getting shot in the grill ( get it? ) becusae the things are so damn flexable, they flex to your cheek/mouth when you get shot there, so it provides for a nice sting.
The i4's do beat the grillz in many places. the vision is better, they never fog up ( unless you want them to which is beyond me ) they dont flex when you get shot, they are much lighter and the lense only sctrach when they take some serious punishment. One thing that i hate though are the ear pads, they are sh1te. i took a hit to the ear, and it felt like a flashbang went off by my face, i could hear jack crap for the next few minutes and was just holding it and moaning like someone had cut my ear off.
Hope this helps