If you go with a lock miter bit, the Lock Miter Master gauge will let you set up the bit and fence position easily. They will work with any brand of lock miter bit. (Hint - you don't need both sizes- the larger one will work for all).
Set up lock miter router bits for perfect joints in minutes, with minimal setup and less hassle!
www.infinitytools.com
I have the Lock Miter Master gauges and have used lock miter joints, but I could never get very clean cuts. Always way too much tear-out to suit me. I went back to cutting spline slots the full length of both halves of the joint, and I cut cross grained splines to fit using my table saw and tenon jig. Biscuits will work in larger mitered joints too. The attached photo shows one of my cross grained spline joints. The miters and the spline slots were cut on my table saw. Then I used my table saw tenon jig to cut thin cross grained splines from the ends of a donor board (the spline is actually the waste from cutting a tenon). Then I cut the spline free and to the correct width using my miter saw and a pre set stop block. The spline width should be equal to 2X the depth of the spline slot in the mitered ends of the box sides.
Charley