I use an Aera 500, and am very happy with it. A £5 GPS screen sunlight shield from eBay does enhance it however.
Good functionality, reasonable battery life if running off internal, okay screen, good GPS reception - and you can toggle it over into Nuvi mode in the hire car at your destination.
I've yet to see any multi-function device, including SD variants, function as well as an airborne GPS as a dedicated Garmin device. On the other hand, it's quite a lot of money for a pure backup.
Insofar as I have one, my Aera is my primary GPS - my (very cheap) backup is MemoryMap running on my Galaxy Note 2, which is also my main phone.
G