I have a new model Fluke 52. It was a good meter until it fell in my mash (just momentarily). I've taken it apart several times to get it working (and was successful once), but it's dead now (shows "CAL?" on the screen, always). So, my advice to you, keep the meter away from water.
I have coated thermocouples that I use in my brewery, so I can't answer your question about them. I also have some of the bare bead ones, but I've never tried to submerge them.