I had a good look at this kit at Overland Expo a few years ago before I built my JK + Ursa Minor for around Africa.
I can say categorically the worst thing about my Wrangler is that it's too heavy, and it impacts how it drives and handles.
I can also say if I had another 18 inches of storage space in the rear, you can bet I'd fill it with stuff. (I have no idea what, but the goldfish always fills the bowl).
The last thing I need is a place to put more stuff, because that is just more weight.
Also if I remember correctly this thing costs around $18k.
For that money you can buy an Ursa Minor AND pay for gas and beer for your entire 2 year, 40,000 mile trip from Alaska to Argentina.
-Dan