i have the 8 weight roller piaggio variator zippy sells. it's nice because you can tune it easier than the stock variator, but it's not much bigger (ramp wise) if at all, and it's pricey. when i bought it i thought i was buying the malossi variator actually, it was a long time ago and i wasn't as "aware" let's just say. i realized that it wasn't the one i wanted when it showed up at my house...but i'm using it these days. i'd definitely say get the mulitvar or the polini, you don't have to pay that much more for an actual performance part.
also, i've never heard anyone talk about the polini variator, in fact i'd never heard of anyone running it. although, i just read on terrydean's blog yesterday that while he was at the polini cup last weekend his multivar "exploded" so he switched to his polini...and it worked really well. i'm looking to get an upgrade at some point though, i'd be interested in the TJT as well as the malossi and polini variators though.