In all honesty, the Dynavin is the better unit, but that should be no surprise since it costs 3 times more than the Eonon.
I say this because the Eonon units can sometimes be buggy with their GPS software, and microphones. Now, if you're a bit computer savvy, that's fine. You can install 3rd party GPS applications, and do software/firmware updates as they become available.
Personally, I went in on a group buy for the E46 model. At $319.. the price is unbeatable, and that was for the updated interface version, that supposedly had all the kinks worked out.
I'd head over to E90Fanatics and look in the Site Sponsor/Group Buy section. The sales rep's name is Carlos, and I'm sure there will be a group buy going on soon if there isn't already.
Dynavin = $1100
Eonon group buy = $329
For the small chance that a few bugs will be encountered here and there.. the Eonon is a no-brainer in terms of value.