I think Grillz are the coolest looking gogs around!
But on top of that they offer good protection just below the neck (which the i4's don't) and also wrap around the back of your head really comfortable. The single pane anti fog lens is brilliant! never once has it ever foged up on me in wet and raining weather, and its super easy to clean off when it gets wet which i love, this is as opposed to my i3 lenses (not sure if theres any difference between the two on how they work/their material) which when you tried wiping off any water from them they'd end up leaving water marks unless if you used a special lens cloth, for the grillz you can use the bottom half of your jersey and its be free of water.
I find my grillz incredably easy to take apart, theres only 6 parts to take apart and its super easy! and I never had a manual with mine
The i4's have a really big field of peripheral vision its really cool, you can see down further then the grills. But what puts me off these is the way you have to really pull at the straps to lock the lenses back into place, I can see people having to go through quite afew straps for i4's, I also don't like the lack of protection under your chin because of its diddyness in size.
With that said the grillz have one major pitfall, if your screaming with them on, the sound bounces right back at you, and this can be DEFFENING! many times i'v poped my own ears when i'v been calling.
Material wise, the Grillz have a hard plastic surrounding the frame and a soft flexie plastic around the rest of it, I'v gotten bounces off it before its that soft.
The i4's are made of a hard plastic aswell in the lens section, but there are some very nice soft ear coveres which i'v also gotten bounces off.
Both very nice masks, but in my opinion i'd go for the grillz, just feels more comfortable when I wear them
