I always find that the i4s are just too short for my long-ass swede. Much of the time when I'm shouting my mouth is completely exposed!
Can't say I've ever used a pair of grillz but those look a bit sexy.
I love my i4's but my mate that has them has a longer/bigger jaw than me and isn't such a fan after getting shot in the jaw while wearing them, depends how long your face is
i personally have a pair of grills as my mate sold me his for 20quid and they work fine and definatly do the job, on the other hand from wearing his i4's they offer a wider range of viewing and are clearer but obviously that is down to the lens