There were a few videos over the past few years from something called "GE Hong" a Chinese woodworking forum on youtube. The fellow has his own FAST way of chopping mortises. Nice when the mallet is halfway into the swing, and he is still moving the chisel...and never misses.
I do have a few older mortise chisels I use.....
Mainly with a mallet.
layout out a mortise, I use the tenon that will be going there. yes, I make the tenons first. I trace around the tenon, while it is being held in place. I use the chisel that matches the size of the tenon. Normally, I work with the bevel away from me, until I get to the other end of the mortise, then a chop with the bevel towards me. I clean things out, and go again. I also tend to sit on the shop stool at the bench while chopping
For doing some types of mortises, I use a jig to hold the "target" still..
Just three boards, I can attach the bottom to the bench either with clamps or screws. I size the gap to match the part being mortised. I slip the part into the jig, and a finger clamp to hold the part..
I keep the tenon handy, for test fits..
These were on the ends. Doesn't really matter where, as I can slide the part as needed. I use the Visegrip clamp because it is fast and simple to use.