Hi, My Daughter had one until our Grandson turned up.
They can suffer with starter gear problems, if they are started with insufficient power in the battery, they can backfire, causing broken teeth on the main starting gear behind the rotor, which can be heard cranking the bike over. On my daughters bike a broken tooth jammed in the stator shorting it out, so I fitted a new starter gear and repaired the damaged wiring and all has been well since, I still see it's new owner riding around occasionally.
As regards tuning, it just needs the usual, less restrictive silencer, open up the airbox inlet and a rejet to suit and you will be surprised at how well they run.
Dave