I have Gianni on one of my alts and I never use it because I can't make it slim enough for me - mainly in the shoulders/biceps. I have my upper body muscle slider set to 10, and for me it's still too big. Can't get that Slink "swimmers build", so I use mostly Belleza because I can slim it up better.
Anyway when I looked at the release, the idea of a MORE muscular Signature body annoyed me (I'm one of the 4 people who bought Geralt because it was thinner and we see how that turned out bleh) so I just logged in to try the demo.
The above pictures notwithstanding (must be the shape they used), the body IS quite a bit slimmer than Gianni (or it can be made to be) - at least the upper body. I slipped it on over my Gianni shape, and the arms and shoulders are *much* thinner. Interestingly, the love handles are more pronounced. The lower body, however, is thicker - the thighs and butt poked through my Gianni shorts. Not too much, but it is clearly very lower body weighted.
I'll play with it more when I get home, I'm at a coffee shop and didn't want to disturb anyone with naked avatars lol, but if one can make a thinner shape AND wear all the Gianni supported clothes, it might be worth considering.