I have seen this one in the flesh, I installed the unit on a BSA B40. The instructions are good, initial timing is easy to set up.
But
The output, as mentioned, is low, not enough to run the standard headlight and the rear running light (not a big issue on a B40 used in daylight), a higher output unit deserves a closer look.
However
The unit has a rather large bundle of wires, they will not fit through the standard grommet in the primary chaincase, so you'll have to open it up and find a larger rubber grommet, and you may be introducing your Norton to an oil leak if you aren't running a belt, which I gather, from an earlier post, that you will be.