[PuckSR]

Read up on GPS.
GPS needs a powerful Amplifier, GPS signals are extraordinarily weak.
This amplifier requires a lot of power. Especially when you have a small antenna designed to fit into a mobile phone.

It isn't horrible though, long term usage is typically done in a car...so a charger is available.
I don't know that I would use this for a hiking GPS system, but then again this phone wouldn't last very long in that scenario anyway.