We have four guys using the Brady BMP21+. One of them was not feeding right the other day, and the guy thought it was ruined from have been splattered with water. Turned out just to be one bad roll of marker or only the roll was damaged from water. None of the others have given any trouble.
We mostly use the M21-750-499 cartridges, and out of hundreds, we've had that bad one (just physially stuck, I yanked it free, cut off the excess and kept using it) and one other where the black thermal transfer material ended up in the cutter somehow.
We bought the kits with the case and rechargeable batteries and they have exceeded our expectations for field use and for small panel construction.