Why are so many Moog Subharmonicons up for sale on Reverb?

Are they terrible? Limited? Boring? Too big? Don't play well (in tune) with others?
I was thinking about one to go with the Spectravox I have.
Thoughts?

For my taste I experienced the subharmonicon way to hard to play with other instruments.
Because of the subharmonic character it can be hard to get musical results if you dont have a deep understanding of music theory, intervals, tunings and stuff.

If you do just noodleing and experimental music it might be a good playground but dont expect to get regular music out of it immediatly.