I have the $79 unit in my 560SL It works fine. It can be attached to the door if you like ( you would buy 2 single units instead of the 1 double) . You do have to remove the door cover to screw it in from behind to make it strong.
I placed the unit in the center console. I would place it in the forward part so that you can use the forward holder without having to put the armrest up. I have to do this in my SL. Prior to screwing it in make sure that it is centered and have at least 1/2 inch from the woodgrain in the front. Make sure you can open the units and there will be no binding.
The 1/2 is to allow for cleaning. You'de be amazed what gets down between the holder and the center console.
Some of the more expensive units are nice, but more expensive.
I am happy with the unit I have.
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car