I wouldn’t use the ones with more than one jockey wheel as you might as well use a rear mech.
If you came downhill were using a fixie aw? a freehub would let your wheel spin.
I think the advantage of non sprung is that you can get the tention you want regardless of chain length. Just check chain tension now and again.
With a sprung unit you can’t really over tighten the chain tension but set it up right and the odd check then it should not slip on you.
I think after riding gears yesterday I’m tempted to wack on a 9sp road cassette on to my ss mtb for the extra speed butt SS is also easy to maintain too.
(Running 18×36-good for site seeing and uphill is easy standing up.)