Not familiar with a starterator, but if it's supposed to be part starter, where's the ring gear?
The starter-generator is a single component unit that starts a motor and then reverts to a generator.
The small engine ones I've seen are belt drive and about the shape of a small car alternator.
Been used on Club Cars, Cub Cadet, Toro, etc
Several older riding mowers with deluxe electrical systems used them.
Newer ones tend to be more compact and have a electrical capacity quite a bit larger than a typical small engine flywheel generator
Kohler, Briggs, etc
They do require a specific control.