score:5
The core differences between a phone app and a dedicated handheld gps are:
So if you don't need any of those features, go with your phone. Personally I'd always take the gps unit and my phone. And while I may log my track on the phone as well, my core nav service would be the gps, and my comms service would be the phone.
Upvote:3
I would say no; your iPhone is not replacement for a dedicated GPS unit when you are in rugged outdoor conditions. The biggest reason is sensitivity. I keep my data off on my phone unless I want to use it, and I have frequently run into situations in which my phone will not acquire a GPS location without first knowing its approximate location from the data service. This was most noticeable in Europe (cities not wilderness) when I didn't have any data access and the GPS would not acquire despite multiple attempts over a number of days. Your phone may be more sensitive than mine, but I wouldn't risk it.
At the very least, test the ability of your phone to acquire a GPS position in random areas when it doesn't already have an approximate idea of where it is from the data service.