Used the gns 5870 today for the first time with the iPad 2
It connected really easily via bluetooth - very simple
Kept the connection with no issues
Air nav pro very good
However, no getting away from the fact it is another piece of kit to remember and to keep charged-although it does come with a cigar charger for which I have a socket in the aircraft-is the same charger lead as used for air box gps and other things.
So my advice is
A -if you haven't bought an iPad yet make sure you get a 3G one
B- go for a bad elf as it is less hassle
C-gns does the job well and can be used where you iPad is not pointing at he sky