I have about 200 hours on my Surefly over the past year. You can have it when you pry it from my cold, dead fingers.
It's installed on the left side of the O-360 on my 172, replaced the impulse mag. The plane was hard to start from day one of my ownership, then would not start at all. Turns out the impulse coupling was not working well for a while, then quit altogether. I was lucky that I was just grounded at my own airport. Those impulse couplings can fail and destroy gears in the accessory case.
The O-360 in a 172N uses a shorter engine mount, so the clearance was tight on the back of the engine--had to remove the mag harness to get remove the battery. Instead of using the Surefly for impulse mag replacement, I got the plain one and removed the impulse spacer from the engine and installed shorter studs. That made it much nicer behind the engine.
I am so happy with the performance of the Surefly. Hot or cold, the plane now starts quickly and easily. Even my non pilot wife remarks that her anxiety level has gone down with the plane no longer being balky to start.
I used fixed timing. With 90% of my trips there would be no advantage to timing advance.
As soon as Surefly gets approval, I will install a second SIM with backup battery.