Dave,
The one I used had the common electronic failure on these cameras that makes them lock up sometimes when you push the shutter release. It would do it randomly, and would last for anywhere from a few seconds to a few minutes before it would start working again. The friend who owned the camera was trying to sell it to me, and he failed to mention it had that problem. I gave it back and said, no thanks!
So, that's my biggest tip: check it THOROUGHLY and shoot a couple rolls of film THE FIRST DAY you have it so you can immediately return it if it does this. Later ones don't do it, the problem was corrected by Leica but I don't think parts are available to fix it now, and the repair was very expensive years ago when I checked into it.
Aside from that, its a neat little camera. Very small and feels very solidly made. Heavy for the small size! It has built in spotmetering and the finder is bright and easy to focus. I'd have bought it if it worked. Since then. I've decided to stick with my Olympus OM gear for SLR use. I like the OM-4T bodies I have and the lenses are great. I am more used to the OM system, having used it since childhood, so I can work faster with it than any other SLRs I have tried. If you get a good R4, it is a great camera though.