Came in very handy for putting in 6 inch locks in 80yr old doors that had already been morticed to suit different sized locks. Probably would have been impossible without it. Only drawback is that to get it to slide on the rails you can't fully tighten both the adjustable rings or else it binds up so you have to be pretty careful the jig doesn't wander off a little. But for the price that's a minor complaint. Using it to mortice into endgrain 6 inches deep was pushing it to its absolute limit and it held up well, I'd another 6 inch lock to do in a 30 min firedoor and it did the mortice perfectly in less than a minute so I can only imagine how quickly this will go through a whole house of standard locks in regular light doors. This jig is an absolute steal at 70e and pays for itself within an hour, I'll probably upgrade the cutters before risking it on faceplate but recommend it 100% for trade use
dan f. 
