I used to own a Velbon Sherpa 600R and decided I wanted a Ball head. I tested out several and the Manfrotto was the perfect choice.
After investigating further before I purchased, I noticed the thread on the tripod was 1/4 inch and not 3/8 inch (basically, half the size)
If I went for the Manfrotto head I would have to purchase an adapter aswell. This unfortunalty made the combo ugly and added unneccesary weight, so I did not purchase it. I also noticed the ball head base was much wider than the tripod head, and would look daft and really not acceptable.
Velbon do there own head with the correct thread size, but it cannot carry the same weight as the Manfrotto.
View for yourself before you buy is what i recommend.
Hope that helps