I have a Contaflex I that I really like. Tessar 45mm 2.8 lens. Synchro-Compur shutter, 1 sec to 1/500, plus B. Flash sync at all speeds. No instant return mirror, you have to wind on the film, cocking the shutter, in order for the mirror to come down for viewing through the finder. Overall, a beautiful camera and a fine piece of machinery. Nice heft to it, too.
There are some things to be wary of. One common problem is sticky shutters at slow speeds. Also, and more of a problem, the aperture fails to stop down like it should--- it's like automatic lenses of more modern times. The aperture stops down, so to speak, when the shutter fires. The springs that control this action are prone to failure, and your camera will therefore only work at f 2.8. This will not be apparent until you get your first roll of film back, and everything is overexposed.
I acquired just such a specimen, however I was able to trade it in on one that had been CLA'd by Jon Goodman, and that particular camera has served me very well.
Some cursory searches on Google should provide you with a more succinct description of the pitfalls associated with these cameras, that's where I first became aware of them, after, of course, I had purchased one on Ebay and prior to its arrival. I was filled with dread while waiting for it to come, and my worst fears were realized. Fortunately, as I mentioned, everything worked out to the good, and as a bonus, that's what led me to the privilege of meeting Mr. Goodman.
If you can get one that you know is in good working order, they are exceptional shooters.
Good luck!