I actually ran across this nifty little gadget while searching for guidance on a flash question I had, regarding a specific issue with my 580x. I did a little research, checked out a as many Google images of examples and figured I'd take the plunge and invest in the grip and snoot.
Now, in all fairness, due to being busy with work, vacation, healing from a broken leg, and life in general, I've only given this a go, one time; the night I got it. Our son was visiting so I told him that he was going to be my test subject (poor kid). So, I messed around with it until I got the exasperated "Mom, are you done yet" question when he had to go (which didn't take long). After he left, I worked with it on a few of my husband's little Fallout figures and then a small antique Dresden bust with some candles. All had different lighting. I tried my poor dog, Sheva (the most beautiful German Shepherd in the world) but she was just not having any of it.
I do like the simplistic, easy-to-use design. The magnet strength is impressive so the snoot felt very secure. The snoot is very easy to adjust when opening it up and is mostly easy to use when collapsing it back down. There is a bit of a struggle getting that last little outermost projection to go back into the collapsed position but it's possible by securing it underneath, so not a big deal. The only real negative that I found is that it seems to not line up 100% (like 99%) and seems to aim just a tad bit higher than I was expecting. For my son's face (bearing in mind it was fairly close proximity, which probably changes much), the beam seemed to aim mostly from right at the the full part of his chin, then above his head and back, even when I had the flash aimed as low as possible. This can also be addressed when off-camera. For the quickness of my first test, I just had it mounted directly to the camera.
So, my thoughts? Well, so far, at least, I'm not sorry that I bought it. I found it easy to use, which is always a plus. I do like how compact and flexible it is, yet also sturdy. I do think that I'll have more luck with it under better circumstances, in a better location, and am excited to try it out. It does exactly what it's supposed to do. It directs light from the flash to the exact place you want it to go, while allowing preservation of the ambient lighting. In the non-serious snapshots I was taking, I immediately noticed the potential benefit (well, probable benefit) of using gels, but I did not use them for my little tests.
The shot of my son was taken while he was just sitting on the couch under tungsten lighting. The figures were on the counter under flourescent lighting and the Dresden bust was on a table in an unlit room with only the candlelight to each side.
Summary: I do recommend it and believe it to be worth the price and will definitely be using it again, "for real".