Take any joinery and throw in an angle and immediately people panic. Now up the ante and make that a compound angle and most woodworkers curl up into a ball and cry. The mortise and tenon joint is the backbone of furniture construction and simple and compound angle mortise and tenon joints are a mainstay in chair making. When cut by hand however, the angled mortise and tenon is no more difficult than its standard brother. The complexity lies in the layout because cutting it is just sawing to a line. The hand saw does not care what the angle is, after all 90 degrees is still an angle.
Compound angled mortise and tenons ARE ACTUALLY EASIER TO CUT BY HAND THAN BY MACHINE. All you need is a saw and a bit of confidence to split a line.