Hello Ouzo,
I had the retractables installed when the car was restored. The ones I had installed were original MB seat belts, and they were installed according to a Mercedes Benz Technical Bulletin issued in the mid 1970's. It is not an easy install: there was drilling and welding into the body, and the chrome cap that the soft top mechanism pokes through needed to be modified and then re-chrome plated.
I love them; I would not own a vehicle without them--I just don't feel safe unless restrained--but that's me. Others of course don't wear any seat belts and some go motorcycling w/o a helmet--it's personal preference.
Since it was a retrofit, there are bound to be a couple of snags. I found 2.
1) The belt tension is strong; yesterday as I drove my car to its winter resting place my left shoulder was actually sore. This could easily be cured with one of those aftermarket pads. Lots of other seatbelts fall into that category which is why they make those pads in the first place.
2) The latch mechanism is on a long "wire", and this does have a tendency to hit and thus scratch the center console wood.
The problem that some others seem to have is the fact that without a B pillar, the belt comes from below. Since I am only 5'8" this isn't an issue for me, but for those taller it might be a problem.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored