I have them, with mixed but overall favourable results.
They do give you more articulation. There is of course a lot of debate about whether that articulation is USEFUL or not, useful being defined as the dropping tire having weight or pressure on it. On a ramp they give you more articulation.
The don't affect road manners much.
They are expensive.
They are said to unhinge too much going up steep inclines. This hasn't been my experience, but I don't point and shoot at too many rocks faces I don't know I can climb (and there just plain aren't many around here). In most other situations they do help articulation (my opinion).
They seize up if not lubed REALLY often. This happened to me.
The Tera ones have been known to break.
I have found that they do give useful articulation. In my case, the dropping tire simply wouldn't droop unless the stuffing tire was FORCED up. This is definitely the experience I have had, but I know others with different experiences. The difference, I believe, is in the springs. These shackles seem to work best with a pretty stiff 4 inch lift spring. With this type of setup, the tire will still have to be forced down. I think (my opinion only) that with softer springs what happens is that the tire has a tendency to droop too easily. All I can tell you for sure is that with my 4 inch procomp springs I DID have USEFUL articulation. If you are really interested in how they work with softer springs, ask me again in 2 months. I'm going SOA, and I will try to revolvers with it SOA at first, and remove them if I don't like them that way.
Keep in mind that you will probably need new shocks, longer brake lines, etc etc, and that it took me a lot of playing around to get shock length and everything correct. I also cut off the spring clamps on my springs.
The reason I am going SOA is because I still want more flex. The revolvers really helped, but due to the stiffness of my springs when the rear flexes it deflects the hinged part of the shackle so much it won't unhinge. Plus ground clearance, blah blah blah. I may go with a combination - revolvers in the front, regular shackles in the back or vice versa. I found they work really well in the front. I'm just going to do what I always do, and f#@! with it till it works!
Overall I'd say they are a useful addition to a SUA jeep that wants more articulation without sacraficing road manners, and an owner who wants low effort upgrades. The guys doing SOA or whatever to get the nth degree of flex are going to be able to tune their rigs better without them, but if you have a SUA lift, don't want to lose that investment (by going SOA), and are looking for a bolt on articulation gain (keeping in mind you'll have to bolt on new shocks and brake lines, too), this is one way of doing that. Yes, they might unhinge blasting up steep inclines, but I'm guessing the type of guy described in the preceding sentence isn't going to find himself in that situation too often.
got to http://www.chadlloyd.rockcrawler.com/Jeep.html
for some more tech details about my experiences with them.
Anyway, let me know if I can answer anymore questions.