The Good: Easy to align. Captive hardware is a big plus. Chain rub is almost nonexistent. Works as advertised - no dropped chains yet.
The Bad: Some suspension linkages may cause compatibility issues - see below for more details.
(This review is for the seat tube mounted low-clamp version of this guide.) I was initially disappointed when I found that the lower linkage on my 2012 Giant Trance forced me to mount this chainguide so high that it looked like it might not work properly. So if you can, you should check the compatibility between this chainguide and your specific frame before you throw down your cash. I had doubts, especially since I was using a 32T ring, but since I started riding I have forgotten all about the installation issues. After a little bit of adjustment, there is very little chain rub. There's some slight noise when I use the lowest or highest cogs, but nothing that I can feel through the pedals. My first ride with this chainguide was down a steep, rocky trail with about six or seven miles of continuous descent. The guide worked perfectly - not one dropped chain. And that's the way it's been ever since. As long as you can get the guide to fit on your frame, the performance is great. Yes, it's a little pricey, but it's a high-quality item.