It will hurt quite a few finishes. Be careful around paints, plastics ("polymers"), wood, etc. I use it as a rinse, essentially. Simply because I can get lazy about wiping off everything after I scrub with my toothbrush. I always oil afterward. The hint of Hoppe's under my toothpaste is amazing the first few times I brush my teeth after a cleaning session.
Oh, it seems to me that it works really well in a .22 bore with all that wax. I don't know if it is actually dissolving it, or just the action of doing anything at all though. Overall, guns aren't that tough to clean...