Weve used these for a long time at work, as a buffer and as a sander with an 8" pad. I work on fiberglass, and buff on gel coat. This is one of the best tools out there for removing caked up anti-fouling on boats, and all kinds of composite fillers. It doesn't bog down like air tools do.  The key to longevity with these buffers is to blow them out with compressed air once you're finished sanding, and I've never had any issue with them by just simply buffing.  Only time we've had to replace them is when one was dropped and the output shaft bent. We tried several other options because we were strapped for cash at the time, but none of them lasted a full year, kind of a shame too, because it wouldn't have been much more to just buy one of these.