Yes, you get low end and top end boost, cause its smaller open and bigger closed than the stock one. It wasnt hard to tune at all. The 4.7g weights that came with it were too light for my non-kitted bike (I had a Leo, 13.13, filter, at the time). I used JB Weld and BB's (~.4g each) to bump it up to 5.1g each, and it works fine even after kitting to 64 Malossi with a cut crank and case matching and a 13mm intake.
I suspect that when I put the rear-end gears in it this weekend I will go back to 4.7g to keep it from opening up all the way so quickly.
As a side note, the strengthened spring that comes with it helps a LOT. You will need a bench vise, a 34mm socket with a breaker arm or cheater bar or something, a pair of vise-grips with the compressor fork end thing (not the normal plier ones) and some patience to get it on, but it's worth it. Mine will get the front wheel off the ground since I put the spring in (if I am standing on the pegs, anyway). Before the spring went in it would surge on takeoff as the variator bounced open and closed.