Mike Harris wrote:

That said, have you ever used one?

I have, and I don't care for them. They're very pricey for what they do,

Ditto that - we have one, it may be for sale (I'd have to consult with
my better half), but I wouldn't recommend it.

IMHO a simple homemade three-bin system is much more useful at a fraction of
the price.

A three-bin (or even single bin) may not produce as quickly, but neither
does the tumbler if you don't crank it and water it very regularly.