This is probably going to be another parts camera. I picked it up from a thrift shop for $10, and it's obvious why it's so inexpensive: it had been dropped (or something heavy dropped on it) and landed on the pentaprism, and if you take it off and look at it, you can see a huge crush spot.
You can still get prisms for them on the used market, and I'm debating about whether to get one. Unfortunately the quick-return mirror is stuck in the UP position. I've been toying with it, hoping there's a mirror lock-up switch somewhere, but so far no luck. A shame, too, since the focal plane shutter still works. Seems to me that if something nasty were to fail, it would be that.
Someone's already been in to it, however; there are little screws missing from the meter collar under the rewind lever. So my guess is that this camera my never work properly again.
As I mentioned on its page, the Sensorex and Sensomat were sisters and very closely related. The difference was the external coupling arm between lens and body; the Sensorex has it, the Sensomat did not. The coupler allowed the Sensorex to meter at full aperture and then stop-down only for taking; the Sensomat required the lens to be stopped-down during metering, which many people find annoying.
This RE was a revision to the original Sensomat. Minor changes include a reworking of the film advance lever and the shutter speed dial. The major change was the metering system, which now turns on when you wind the film and by using the single preview button (bottom right on this photo), whereas the original was a two-button affair and rather confusing.
One of Modern Photography magazine's Top Cameras
Camera manual: Orphan Cameras.com
Modern Photography magazine camera test: June 1971