What advantage does the synchro spark have over the mechanical advance?
I have a Brison 2.4 with the mechanical set up and it starts and runs great.
I have ordered the 3.2 and Harvey said there is no loss or gain either way.

The early A&M mechanical advance, copied by almost everyone, was a "Rube Goldberg" system that has unnecessary bell cranks and links..All these parts can become loose and sloppy(or dirty and tight) and cause uneven timing..The advantage of Syncro Spark is elimination of all these moving parts, and ease of installation on engines(mostly twins) that don't have a direct path from the carb to the moveable ring on the front of the engine..
There is only one reason for the links and bell cranks between the carb and the moveable ring..Engine manufacturers are too tight or lazy to make a carb insulator block to rotate the carb. and a new arm for the throttle shaft..
Horizon, after years of selling engines, has come up with a revolutionary new piece of bakelite to do exactly this..(at the owners' expense, of course)...My first conversion, in 1987, had this, still do, on all engines....RC.....

I added syncrospark after I crashed and bent all the linkages on my 2.4. It ran the same, just no linkages to wear out or get out of adjustment.

SLC

1: Easier starting if your engine has a magneto.
2: Some have reported a slight RPM gain, I did not.
3: Once timing is set, it usually doesn't vary
4: No moving, vibrating parts to wear.

I converted my G62 from the hard cranking magneto to the Synchro Spark, and it has been a joy to work with ever since.

Vince