I have most of the models, including the SL 35. It's a throwback camera that was behind the times when it was introduced in 1970.
It used stop-down metering when others had moved to open aperture metering. It didn't have a split-image focus aid in the viewfinder when others were offering that feature. It lacked a true hot shoe - again, others were offering that as a standard feature. There is no aperture or shutter speed information in the viewfinder when others were starting to introduce this.
There are two types for the SL 35 - those made in Germany, and those made in Singapore. Functionally, there is no difference between the two, although the "Made in Germany" models usually command a higher price. Both are available in satin chrome and all black.
I've used the SL 35 (Singapore) for about five years and enjoy it quite a bit. It's a very basic camera. You set exposure, focus and take your photo. The camera was sold with a small cap for the shutter release. That usually is missing today. I've found that a soft release does help this camera, because the release is a very thin post.
The reason to buy this camera is for the Carl Zeiss lenses. The Rolleinars enjoy a good reputation. The Zeiss lenses should be a notch above them. The earliest lenses are single-coated, I believe, while the later "Made by Rollei" optics use Rollei's patented HFT coating.
There's nothing wrong with the Rolleinars. I just think that the reason to buy into this system is for the Zeiss lenses. Otherwise, any other camera should fit the bill.
The f/1.8 Planar is excellent. It served as the basis for nearly all 50mm lenses at one point.
The good thing about these lenses is that they tend to be less costly than their counterparts for the Yashica/Kyocera Contax system, although they still command decent money and almost always more than the Rolleinars.