I only use Sportys E6B app to avoid the dreadful whiz wheel (on my iTouch V 4). Also have a free TAF / METAR app called Aeroplus.
I'd suggest that the screen is too small to use an iPhone for serious GPS.
I've flown in the US with a guy who has sectionals (and everything else) an an iPad and I don't think anything smaller is a runner if you have to look at all the other things at the same time.