So I looked at the photos of this and thought "that doesn't look like an amp". And sure enough, it isn't. It's the effects board from an old Wersi organ, which someone has very nicely rehoused in its own case with a footswitch.
It uses bucket-brigade delay chips to do chorus and rotary speaker effects, which are switched with the R and C buttons on the footswitch. I think the D and P switches are for Deep and rotary Fast/Slow, though they don't act quite like I'd expect.
Sound-wise it's really just different flavours of chorus, although the rotary does a nice speeding up thing when you kick it in. The rotary effect would probably sound more convincing if it was in stereo.
Whoever made this put a lot of care into it!