Nice little finder. I can't tell the brand for certain, but it may have been fashioned from parts. There is an Orion 90-diagonal, a separate eyepiece (around 12-15mm, I think), and an approx 50mm objective lens.
That makes this somewhere in the neighborhood of a 12x50 finder, open to revision (by changing the eyepiece).
Rings and mount included for $50 shipped CONUS
Incidentally, the finder bracket seems more for a Dobsonian or Newt reflector - ie., you may have to drill a
hole in the OTA.