I persevered for 6 exchanges. 7 phones in total, yes seven - which was getting a bit ridiculous and taking too much of my time too. Every unit demonstrated the same random errors, ie. unusable position services data (jumping around in Maps/Gogle Maps and jagged zig-zag positioning in sports apps, eg. Strava, Endomondo, etc, etc).
Cycle rides 10-15% longer for the obvious reason:
Everyone has their limit with patience and frustration, and I'd exceeded mine - plus, despite technical demonstrations of the faults, the manager at my local Apple Store was starting to get a bit of an attitude frankly... so I walked away with my refund and am back to using my old faithful iPhone 4 for now until such time there appears a confirmed fix.