I just received the new Finesse Generation 4 diabolos from Mister Babache and of course I started to juggle immediately. 
Photo: Finesse Generation 4 (left) Finesse Generation 3 (Right)
The feeling is great. The diabolos are much faster, less slowing down than Generation 3 and also much more stable because of the new features.
It is more comfortable to start multiple diabolos (3,4,5).
Some changes : The Generation 4 Finesse diabolo weights 270gr (15 gr heavier then G3) , the cap shape is rounder , the new V shape axis is amazing. You must try it. It is hard to express in words.
Ofek Shilton
