but how hard is it to adjust the timing on one of these and how do you check/change it?
The easy no math timing.
Cut a strip of paper 1/4" x 5".
Rap the paper around the prop drive, back by the crankcase where the magnet is. Overlap the paper then cutwith a #11 blade cut though both layers of the paper.
Now you have a piece of paper the exact circumference of the prop drive.
Cut it in half, take one of the halves and cut that in half again, take that and cut it in half also. Now cut it so it'sin 1/3 and 2/3 pieces.
The 2/3 piece is how much before TDC the engine should fire, (30*).
Now find TDC by removing the spark plug, then sticking something in the hole, a pencil works fine. Move the crankshaft until the piston.is at the top of the cylinder, you'll find that about 5* either side of the TDC it doesn't feel like the piston is moving. Wiggle the crank back and forth until you can find the center of this piston not moving zone, that's TDC.
Now with a marker make a line across the edge of the prop drive onto the crankcase, it doesn't matter where, just that it's easy to see.
Now turn the prop drive clockwise a distance equal to the 2/3 piece of paper.
Plug the ignition into a 4.8v battery, and turn it on.
Now with the two screws loosened move the sensor off the magnet until you hear the ignition pop.
Tighten the screws for the sensor down, then confirm that the timing is still set that 2/3 piece of paper before the TDC mark.
You may have to lengthen one of the grooves in the sensor mount to get the timing correct.