I’ve used clear screen protectors on all my iPhones, and they do a damned good job, providing you apply them carefully, with no bubbles or fluff. Only the edges are noticeable on mine, there’s no evidence of anything on the phone at all, plus I have a clear case like the one Kryton has, cost about $4, and it’s already saved my phone after I pulled it out of my pocket with the power cord while charging with a back-up battery, and the cable pulled out! It cartwheeled several times down a steep Tarmac road, and only showed a tiny mark on the polished front beveled edge, so very well worth having.
I do have a totally enclosed case coming, which will seal the phone in, making it waterproof and shockproof. It’s a Kickstarter project from TacTic, who made the first alloy watch straps for the last Nano. Not cheap, but comes with Gorilla Glass screen protection. There’s a good Otterbox available, too.
Overkill, perhaps, but I spend time near the coast, and salt water doesn’t enhance the performance of an iPhone 5 particularly well.