I've had a few of these kits (not from Buzz) and with a fair bit of fettling they do give good performance and value for money.
The Buzz. kits are tidied up before he sends them out I understand so thats less work if you're not that inclined.
Personally, I try to get hold of just the alloy/ sleived metal barrel and get a piston from Scooter Restorations (Mahle- £30 or so), and then get my "borer" here in Bristol to bore to fit. I've now gone down to 2 1/2 thou clearance and this does eliminate any "slap"- the alloy/ metal bore seems quite forgiving at this close tolerance and I've experienced no nip ups to date..........
The beauty of these cheap kits (and even cheaper barrels) is that you can have a play yourself tidying up the ports etc- if you screw it up, they're cheap to replace
Chris
Scootering since 1968.