I bought one and used it a few times. I thought it may be fun to try. I ended up not really caring for it, though. You can certainly cast dry flies and get a really great drift, but that's really it. If the stream you're fishing is brushy or has any overhanging branches, you can forget about it. Unlike with a regular fly rod, side arm casts don't work, so there's no way to cast under anything, and your back cast is always big and open, so I always was catching branches on the back cast as well. Managing the line is also a hassle! It's long, and you can't just reel it in when you want to move to a new spot.
I never hooked any sizeable fish, but it is really tricky to bring in even smallish fish because of the length of the rod.
I also think it would be great for fishing for sunnies or something - basically just using it as a dapping rod. It may also be fun to have on a backpacking trip because of how compact it is when it's collapsed.
I never tried nymphing with it, but I could see high stick nymphing working. Only problem there is that the rods are really flexible, so chucking heavy nymphs may be a problem.