I've used mine without complaint as a hopback. The trick seemed to be to start the drain from the kettle very slow and then open it up slowly. The problem is that I went so slow that by the time the wort got finished the temp had dropped enough to the point where I wonder how much hop utilization I will have realized from it. I used it two weeks ago, so we'll see.
Regarding using it as a Randal, I did not have a good experience with this (yet). I only used about 2 Oz of cascade leaf. It clogged immediately. I took it apart and dug out about half of the hops and put it back together with equally poor results. Oddly enough, I don't think it was the hop blocker itself that was clogged, because when I took it apart and disconnected the output tube, I saw that the little nipple was jammed up tight with hop sediment. I had to dig it out with very small screw driver. So it's like the randal wasn't blocking enough hop sediment. I think maybe the pressure in the keg was too much. I had pressure down to around 10 but I think maybe I need to really keep an eye on it and start much slower.
Anyone else have experience using one for a randal?