Designed to the amateur market the Contaflex was an excellent option for those keen to enjoy the Reflex feature without paying about the double by a Contax reflex our an Exacta Varex. The system had several lenses and accessories. The lens rear elements are part of camera body. To go from 35 to 115 mm only the front elements are changed. But this doesn't save weigh or size compared to Voigtlander or Kodak reflexes, also from the fifties in which the whole lens comes out. It uses a leaf shutter that it is perfect for flash synchronization up to 1/500. It is a pity that you can't hear how silent it is due to the not so discrete "clap" of the mirror.
There are backs you can buy and change while loaded with film,but nowadays they are so expensive as another body. Meter is uncoupled. It is a nice camera to use but it has its idiosyncrasies: to focus it is the same ring with two nobs (see picture) whatever lens you are using. This is not very comfortable mainly with the heavy 115 mm hanging on it.
Comparing rangefinders to modern reflexes the first ones are are much easier to focus under low light conditions (when coupled with telemeter). On top of that a rangefinders does not blind you at the very moment you fire (for reflexes it is either you or the film). So the aparent "what you see is what you get" of this system is ironically not true exactly at the moment you are actually taking the picture. This makes a big difference in low speeds and when using flashes. But this is for modern reflexes, for the first ones like Contaflex, Bessamatic end Retina (the ones I have) this was even worse because the mirror doesn't go back to position. The moment you press the shutter you say goodbye to your subject. You will see it again only after winding another frame. The only reason for the success of this system for me is due to no paralax error whatever lens or distance you are shooting and that you can focus always in the same viewer, the same way. Nowadays with modern paralax correction and auto-focus rangefinders are coming back. You can have look also on the   Retina Reflex III  from Kodak and the   Bessamatic  from Voigtlander.