There are good GPS units with bluetooth connectivity available on e-bay. Get last year's most-popular model, and you'll probably find it cheap, and working fine.

I've done comparisons with my Belkin F8T051 (bought used, on e-bay) which gets fast locks, and is incredibly accurate (even in Manhattan and Brooklyn - skyscrapers and ELs are just hell on GPS). My N810 has me wandering across streets, up through buildings, while the Belkin has me +/- a few yards. (I use Maemo Mapper and tracking to review).

If you're hiking, it mayn't make much of a difference, but operationally, a separate bluetooth based unit is much easier to deal with. I can put it in my pocket when getting out (of the house, car, subway) while I get M.M. started up - and typically I've got a lock by the time MM is up and going. When driving, it is nice to put the GPS up on the dash, while keeping my N810 in a more readable position.

Overall, I guess, given the weak "locking strength" of the Maemo, a separate BT attached GPS unit is a *lot* easier to deal with in general....

I should mention also: I use this GPS unit with a couple of different devices. I originally bought it to use with my Palm pilot (and Mapopolis), but it's come along with me to the N810. I actually have a dedicated GPS unit, but frankly have used it so rarely. The GPS unit seems to do only ... GPS things. By packing one more pack-of-gum sized item with my usual gadgetry, I get "free" GPS. I'd prefer to not have to go online for directions (with M.M.) - but that's the only drawback. For interactive mapping and such, MM is great - and is fine for not too complicated trips. I do miss the dynamic re-route capabilities of real GPS units - but I need that about ... twice a year?