i made some heads back in the day that really helped with the 70 air cooled kits, they don't have enough fin surface area for the power they make and they have such a bad chamber with the decomp valve and shit in there that they burn really inconsistent. they are slow to burn off the pipe and once they are on the pipe they detonate like shit.
there are only a couple 70cc heads on the market that *look* good IMO, i haven't run them because i always make my own but the malossi no-decomp head for 70 and the doppler for 50cc are the only two that look halfway decent.
i dunno what to make of that polini but the one i built a few years ago had big casting boogers all up inside it and no real quench area.
the problem with all of them (including the two mentioned above) are they have WAY too much squish area for the pistons that come in these kits. Maybe if you had a flat top piston but you really need to have more combustion chamber volume to keep them cool with a big french pipe.
i'm not a french expert by any stretch of the imagination but my conclusion is: 70 cc with a stock pipe, low rpm, low compression, big torque and cruise OR 50cc balls to the wall high rpm big pipe and do everything you can to keep it cool/alive, there is no in between.
i actually kept the stock pipe on my TSM with a 70cc airsal kit, SHA, stock variator. Dont' have a lot of miles on it but feels good.