Yep, I have one, it has been a steep learning curve, with quite a few bits needing to be replaced. The biggest weakness in the design is the clutch bell, but I've resolved this finally I think.
The engine is quite good, very good on fuel - 45Kph is quite achievable on the flat. Very easy on fuel too, and uber quiet. Has a 200W sticker on it as well, so that makes it legal doesn't it.
Once it was run in, with 10W-30 Penrite oil, and running on premium 98 octane, NGK sparkplug and highflow air filter (ie. its current condition) it uses 1 tank of fuel (900cc's - at 1.50 per litre = $1.35) per 60 klms, with the average speed of 45-50Kph on the flat easily. Its great fun on the road, and even more fun to throw on the offroad gear, and do some bush bashing!
I have changed a few things from the original design, due to 'teething problems' I experienced with the kit (now all sorted).
1) The original design didn't suit a bike with caliper brakes very well, it had to be tilted back so that the belt cleared the brake mounts - The problem with this is that you couldn't fill the fuel tank more than 1/4 full or it would leak in the heat (out the vent on the cap) and you had to hold up the rear of the bike when filling the fuel tank - this has been fixed by making new fuel tank mounts that allow the filler to be on the exhaust side, rather than the intake side. You can fill the tank all the way up at the service station now!
2) Replaced the supplied bolts that hold the motor to the main frame with longer ones, better lock washers and nylocks after the stock ones came loose and the belt shredded against the mount and snapped (and broke the crappy plastic belt cover).
2) Replaced the fuel hoses (the rubber one goes hard and cracks, just sucks in air) with silicon TYGON hoses (the best).
3) Replaced the fuel filter with a smaller one from a whipper snipper as with the old one, and a low tank of fuel, the filter starts sucking air in corners and the engine stumbles/dies.
4) Changed the sparkplug from a chinese no-name to a genuine NGK CR5HSB after it developed a misfire.
5) Replaced the carburattor diapraghm + seals with a genuine Walbro WYK rebuild kit to fix a surging/flooding problem.
6) Applied blue locktite to all the bolts that keep coming loose on the engine ad-nauseum due to vibration.
7) Replaced the standard 'thin' belt to a thicker one - better for offroad use (11 tooth has much higher torque - broke one of the thin ones with it).
8) Fitted a highflow air filter - made about 3 kph difference to the top end speed.
These fixes (most of which should be applied to any of these blackstar kits) have improved the reliability and performance of the kit so that it may be ridden daily - I also have an 11 tooth sprocket which allows greater hill-climbing ability, but reduced top speed - its great to take the bike off-road through the bush - top speed with the 11 tooth is about 35-40kph. Range is decreased to about 40K per tank due to higher RPM's.
The motor runs a 76mm clutch (identical to the pitbike motors) so if you wish to do some serious offroad powerups, one of the $100 49cc 2 stroke gokart engines (2hp) and the 11 tooth gear should have you climbing trees.
I'm selling it if you are interested - looking for around $300 or so...