Although there are lots of two wheelers about in SF and car drivers there are at least somewhat aware of bikes/scooters/motorcycles a MSF course probably isn't enough training for getting to be profcient on SF streets, but what are you going to do?
A rite of newbie passage in SF for any two wheel rider is the process of going down because of inappropriately hitting/crossing the Muni/cable car tracks, especially when wet.
As far as a particular scooter in SF, I've had a S90, a CT110, and some Passports, none of which is a scooter, but are indeed pretty ideal for SF. Any hill a Passport can't go up is too steep for a new rider on a CVT scooter.
All makes of scooters and bikes get stolen there, with old Vespa's/Lamretta's maybe at the top of the list. Get a cover (lots of salt air with the fog) and make the cover ugly, and lock the bike to something, if you can, with a heavy duty lock where/whenever its parked. For some reason there is a 15+ year plague with sparkplugs being bashed/stolen in SF. Something that has a cover for that is a help, too.
Bicycles are pretty handy in SF, but are really not much safer than scooters, if at all.