Hi Dave,
The Boyer is smooth but it only has a 20deg advance curve, which means if you time it at 36deg full advance, the 'retarded' position at start up will be 16deg btdc which could give you some kick back. I believe the Wassell units are pretty much the same.
The Boyer MD which I assume is the MkIV has a 32deg advance curve, so if you time it again at 36deg full advanced, the start up timing will be at 4deg btdc, so should be much easier to kick.
The 'ski' jump at the bottom end of the rev range on both the Boyer MD and the Tri spark is an anti-stall device which advances the ignition slightly to make the revs rise before the engine stalls.
Jim