Fan clutch options

daves66valiant said
Although it does not spin easily it does spin.

That's how it works. Yours is both speed and temperature dependent.

daves66valiant said
I curious as to how these things would fail actually.

My personal experience has been failure when worn - they get sloppy and wobble.
However, regardless of make, sometimes they will fail when fluid drains out or similar and spin freely as Steven posted.