I livein a ~20 year old townhouse. My old shower valve leaked behind the wall with no symptoms in the part visible during normal use. Lots of damage to the drywall around it and a 2x6 support for the valve before we discovered it. After taking down the tile and drywall we saw the mixing valve itself was leaking, and that it had shutoff valves for both hot and cold input. I immediately turned off both shutoff valves, only to find that the left side shutoff valve itself leaked. Luckily, it seemed to fix itself after a draining maybe 50ml into an improvised catch-can. I think maybe it was just backward drainage of the water column in the part above the valve (?).
So now I have to put in a new valve and a couple of these shutoffs, I suppose. I understand most valves these days come with threaded interfaces? So this usually means sweating together an adaptor of some type, then screwing that into the valve properly, then sweating the other end of the adaptor onto an approprately disassembled/cut supply line.
Is this correct? Except that in my case, I will sweat in these cutoff valves after the adaptors or as part of them. I like them. I will install them facing backwards, though, since if this ever needs to be accessed once the shower is assembled, it'll be from behind.