That is certainly a cheap item and good value for the money. I've owned a few cheap Chinese GPSes and head units, so here's my thoughts:
1. Screen resolution is a lot lower than the Nexus or any other branded tablet
2. these sort of units have buggy software and the GPS may randomly crash. Won't have Googlemaps which is by far the best mapping/GPS system I've used - mainly due to the POIs not being limited by the map producer's interests.
3. Does it have an audio line out (ie. 3.5mm stereo plug)? Although you may be able to use the Bluetooth to send an audio signal to a bluetooth receiver (eg. Belkin Aircast), it'd be preferable to get one with a line out too as a backup.
4. It's unlikely the audio quality will be any good.
5. Audio via an FM transmitter sounds shit - often worse than radio stations - I would never rely on this.
6. I'd assume that if you have your phone connected via BT and playing music, the music will pause when a call is received.
7. Battery life will be rubbish. I'd be surprised if you get 2 hrs from new. I'd bank on having it plugged in all the time.
8. No email, internet radio, no data search capability - may not be important/useful?
9. Parrot BT kit will cost you $200+ (extra if you need someone to install). I'd be inclined to spend more on the unit than on adding BT.
10. 128MB RAM in this vs 1GB in the Nexus 1 / 2GB in the Nexus 2 - might not be very stable?
11. Reversing camera is the biggest selling point in my view. But I'm pretty confident there's a way to hook this up to an Android tablet (or rather hoping an app will appear soon?!

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I think there's a reason why people chose the Nexus over other devices for an install. You can pick up a 1st gen s/hand for about $150. I'd suggest doing that instead if budget is a limitation.
My 2 cents. Hope that helps somewhat
If you're just looking for a cheap BT unit and already have the aux in plug installed in the car, I have this and pretty happy with it for the price:
http://www.kogan.com/au/buy/home-stereo ... oth-audio/Only downside is that when on charge, it turns the device off. But the battery life is reasonable for its size and can recharge in the car.