I've got a Larini on my 99 VT. The sound is amazing - my favorite by far. You can listen to some videos and decide for yourself here:

http://www.quateams.com/ferrari/CG1204/index.html

I can't really comment on the increase in power as the exhaust was already mounted when I bought the car. My car also has the second set of cats replaced with Larini test pipes (the first cats are still on).

There's no question about the weight savings. The last owner gave me the OEM exhaust and it's like a steamer trunk. Completely ridiculous for a supercar to have a muffler like that.

I believe you would have significantly better low-end torque with this upgrade as the motor is flowing more freely at all speeds. Again, I can't comment directly since the car came with the exhaust, but I have no complaints.

I don't have any experience with Tubis on Lambos, but my Ferrari F355 spider has a Tubi exhaust which I find very disappointing. It is much louder at idle (which I didn't want), but not very different sounding at higher speeds (which I did want - looking for that F1 shriek). In fairness to Tubi I still have the OEM cats on the car which also affect things, but I wouldn't spend the money on the Tubi again. I have an Ansa on my Testarossa which was cheaper than the Tubi and sounds dramatically better (again, though, with test pipes).