re: Square Hole Punches

I use them.

Much quicker than laying out a square. What I do is mark the center point of my plug, then drill a plug-depth hole with a bit that matches the hole in the proper LV chisel.
With the hole drilled, I place the tip of the same drill into the hole and slide the LV chisel over, then use a square to align it with some edge. The drill bit usually will extend way beyond the LV chisel's end so I have a deep socket handy that will slip over the bit and make contact with the chisel. A few taps with a mallet will set the chisle.
]I then remove the bit and wack more with the mallet until the curves in the apexes of the chisel hit the wood/
Note that the pilot hole also allows the wood to push into the hole so you are not enlarging the  desired square hole OD.
With the LV chisel removed you now have nice reference pits to use a standard chisel to finish up the sides of the hole.

 Note that the LV chisel is really just a power mortiser chisel with a screw on basher. If you have a set of mortiser chisels, you can do the same.