Thanks for the info guys - I think I'm beginning to sway towards the Aware GPS now.
Thought I'd say though: With regards to the type of GPS Memory Map uses on the iPhone, the software is dependant on the hardware and the iPhones use an AGPS chip which I wouldn't rely on working too well in the air as it uses cellular data as well as GPS to determine your position; hence why I mention the TomTom cradle.