Never tryed one but heard good things about the Harry Barlow tuned standard barrell. im sure someone else will be along soon to shed more light on this or you could try a search
polini will need a 122/123 main jet and is a grunty bugger to ride, makes a standard one feel broken. simonini pipe would be better on both kits but the sip road is quit and nice all the same
Choice of kit depends on how and where you plan to ride. I have both kits. The Malosi is great un round town, quick off the mark and very revvy. Where as he Polini has mor grun and cruses with less stress on the motorway to rallies.
Malossi 210 revs well, Ali barrel and head. Can be bolted on and will be ok. Very quick kit..70mph+ if set up correctly.
There are 2 types of Polini 207cc kits now. The original cast iron barrel and and exact copy now in Ali. Both are good kits and set up correctly on a Dyno will run all day long. I have a std eng with auto lube and std carb with the iron kit just bolted on with an expansion pipe and that is very torque and put out 15.5 bhp on Diablos Dyno.
The thing with all of these kits is they are designed to run with ported cases to get the max out of them. Port the cases with a good pipe and you should see 17-18bhp with a std carb. With a bit more work to the crank, a reed valve and a dell onto carb and you can get 20+ bhp all day long.