This is a real jewel of a camera. I bought it for $10 from a guy in West Virginia. But that wasn't the best part.
The best part about this camera is that it takes great photographs. The Tessar lens on this camera is the same as the one on the folding Ikonta 35, Contina II and Contessa. I don't mean it's similar. I mean it's the same. You can take the lens elements from a Contaflex and swap them with the lens elements from one of the other mentioned cameras.
On the Contaflex, the Tessar is a real joy to use.
Despite not having a rapid-return mirror -- the mirror flips up and stays up until the film is advanced -- the camera is very easy to hold. It's smaller than its contemporaries, and all of the controls sit where they should be.
The leaf shutter is quiet, but the mirror raising action isn't. Don't expect to use this when discretion is necessary.
Outdoors, this camera shines. Objects easily snap into focus on the fresnel screen, which has a split-image spot in the center. Once properly serviced, you can focus this camera with one finger.
Shutter speed and aperture selection are simple. This camera uses the standard Contax spool, and generally, these cameras come with the spool. Loading and unloading film requires removal of the back, just like a Contax.
Like most Zeiss Ikon cameras, build quality is very solid and excellent.
I've also used this with a Proxar close-up lens and a Teleskop lens and was very impressed with the results from both. You could do a lot worse than a Contaflex I.