I recently aquired a 2000 SLK230 Mercedes Benz which my daughter drives. She had no interest in the OEM tape deck and CD changer so I bought a mechless bluetooth Kenwood head unit for about $150.
Installation was a breeze as the Merc has standard ISO connector for the stereo. It needed a Kenwood / JVC to ISO adapter (about $15 at Supercheap) and a Euro antenna adapter. Plug them in and push the unit into the dash and its finished. About 5 minutes work. No soldering, no wiring. It works fine with the OEM Bose amp and speakers. Tweeters and mids in the doors. Sub woofers behind the seat.
Sound is really good.
Going to do the same for my wifes SLK which has a 2006 Apline iPOD stereo in it - even displays cover art in colour - but no bluetooth.
Jim