I'm still very happy with it. The latest software update added a few little features, I guess they'll continue to gradually release various bells and whistles. It's pretty reliable now, compared to when I first got it, and it had a nasty tendency to crash from time to time, or stop updating the mapping on the screen. I've updated it two or three times now, and after the first one the "crash-ness" of it improved dramatically.
I don't see any reason why it won't work with NiMH batteries, especially since Satmap sale them on their website! The LiIon battery probably lasts longer, but it does cost £30 (incidentally, if you are happy charging it using a laptop or PC, you don't need the £45 power bundle, it just provides cables, a mains charger, and a car charger in addition to the battery). Obviously with NiMH AAs, you'll have to remove the batteries to charge them.
The latest software is Version 1.3, if you haven't got it, it's worth downloading it from the Satmap website.