I've tested XF admin system a while back and i wasn't pleased with its structure at all. What i didn't like
1. I went to test the template system of XF and it was messy for me to play with. Its structure was different than VB. I didn't find it user friendly but all over.
http://youtu.be/BeFO1ZUmBCU
2. Then i was curious about user + usergroup and it wasn't like VB at all, they are missing many of VB default functions but that wasn't what i didn't like, the permission style and how it is structure is very limited and very bland when you create a new usergroup.
I wasn't pleased with the admin system at all, now comparing VB 5.x admin system with XF i think VB 5.x has great potentials and beats it, Vb just need to work hard on their features , functions and front-end designs. And most importantly make use of interactive design.
http://youtu.be/YTjlRoLdmxI vs
http://youtu.be/4zuj6GZi17Q