It's a fine choice...
NTG2.5 has built-in Bluetooth so works with BT phones, including the wheel buttons.
In fact,
all the wheel buttons plus cluster display work 100% as they should.
This replaces the older Convenience Telephony option, thus leaving you with the deep storage space under the centre arm-rest, which you would have been robbed-of if retro-fitting the original MB Convenience Telephony (that, plus a tidy sum as the MB Convenience Telephony kit isn't cheap).
The downsides of BT is that (a) the phone is not being charged at there is no cradle, (b) you don't benefit from the car's external aerial and instead use the phone's aerial, (c) Convenience Telephony had the option of reading-out text messages, which BT does not support.
Oh, and you will need a Mic - which can be discreetly fitted next to the base of the mirror (I believe that the original Mic would have been fitted inside the rear-view mirror, but I am not sure).
As for price... I had mine professionally installed by Alfie and Richard, and the unit was a brand new MB unit (came in a nice new MB box), with 1-year warranty, so obviously not as cheap as some of the second-hand eBay units (which interestingly all seem to come from Latvia for some reason).
Alfie and Richard:
http://www.comandonline.co.uk/