I have iPhone lenses and enjoy them for instant photo sharing. I got the four lens pack with wallet from Photojojo. However, the wallet isn't nearly as handy as I thought it would be, as the lenses often fall off of the magnetic strip in there, and it's just a pain to use in general - much easier to store in the pocket and faster to get it out for use that way.
I do have the 10-40mm telephoto lens, and while it works well, it requires a special case. Since I have my iPhone in a Lifeproof, I never use it because it is too much of a pain to take a Lifeproof on and off, and I'm not going to sacrifice the safety of my phone because just my luck, I'll drop it. The magnetic rings work well with the Lifeproof, though - I just put it over the case. They do not work with the Otterbox (at least not the 4s... I think they changed the case with the 5).