Do you speak from experience using lock miter bits on speaker cabinet sized MDF panels? I know you have more wood working experience than I do.
I have not. A friend who had just bought one of these bits invited me over to check it out. His project was to make make some "faux solid" 3" X 4" cherry (table) legs using 3/4" thick hardwood. I played with the boards and fit-up before we glued them and was impressed with how, just using my hands, I could press fit them together (no glue) and they would hold together to make a pretty solid box just from the accuracy of the fit! I feel completely confident you would not smash or tear mdf when assembling. However, to answer your question, we did not route mdf.
Downsides were:
1) It took a bit using test scraps to get the bit height right so the miters met perfectly on the corner. However, he now has his final test sample to use as setup gauge to get close for the next time. It won't be perfect because the objective is to align the center of the cutter to the center of the stock and 3/4" is not always .7500"
2) He had some tear out at the thin point of the corner when he had to feed the stock cutting against the grain. We took care of that by making 3 passes (when the cut was against the grain),such that the last pass was only cutting less than 1/8" (IOW, a "finishing cut"). Of course this is not an issue with mdf, it cuts very clean and doesn't have a grain to cut against.
