I haven’t so much as marred a fitting since I screwed this on the end of my gun. The hardened jaws go on and off like they’re supposed to, and because of that spring-loaded lock, you can clip it on and run the grease gun with two hands.
I still keep a standard coupler on an old gun I have, but I hardly ever use it. For antiques, off-road equipment, farm stuff, and trailers, this coupler is the one to have if you ask me. The thing never pops out and makes a mess, and I never damage fittings (or the item they sit in) any longer. I even have a few drive-in style grease fittings that make me wince when I used to use a “normal” coupler on them, but with this LockNLube coupler, there’s no chance of damaging even those.