I'm not a Neanderthal by any stretch of the imagination, but I just used 1/4" Narex Mortise chisel from LV for the first and wow, it's a life saver. I haven't even got it spiffed up yet, just out of the box (or brown cardboard envelope). Built a drawer with box joint joinery and had underestimated how long the drawer bottom slot should be on the front and back and didn't notice until I had three sides glued and was fitting the bottom. Not sure if that slot is technically a mortise, but that 1/4" chisel fixed my problem in nothing flat!