I have the 4 of them and the last has always been the best
I keep the N810 in the car for Navigation (N900 is not very good at that yet I think) and it got a new battery for that purpose.
I tried Mer on the 770 but I don't see that going anywhere (not enough power ...)
N800 is used for debugging and testing Diablo version of PWSafe
And the N900 is always in my pocket and ready to use