My buddy built one and I borrowed it. Got nothing but foam for half the keg, so I gave it back to him and don't plan to ever use one again. If you can find a way to get all the air out of it you could have fun from it, the beer did smell pretty great after running though there...you could smell that beer being poured 2 rooms away.
Just tried a beer put through one of these over the weekend at Bootlegger's Brewery here in OC. They were using centennial and cascades, with an APA going through it... pretty good! Not as intense as I thought it would be, but I don't know how long it had been in use. The sample that I had poured normally, and was carbonated just fine. I can see how it would be pretty challenging to get it to be balanced just right though.
I didn't see their "hopinator" as they called it, but I heard the guy say that they basically had a hop bag in a water filter housing. The only other thing you would need to add is some sort of tube inside it that runs to the bottom, since both of the ports on those filters are on the top.
I go to the DFH Brewery a lot and that thing is amazing. It is an absolute must try, at least once, if you like hops. As to article on the DFH website points out - I had a pint of 90 minute run through randall and it was amazing..
I made one of these and typically break it out during harvest time in my hop garden... does tend to foam a bit if your beer is over carbed... but once you get the thing flowing it delivers a real treat!