I have 2 Mariner furling units on my Bayfield 32 (cutter). They work well if maintained. Everything can be dissembled, cleaned, and lubricated. I just use boat trailer wheel bearing grease. I can see where they might have a problem on a long luff, but on my 32, no problems. A nice system that allows easy sail changes *and* furling (but not reefing).
Steve Dashew had (and still has) good things to say about them. Hope it helps.