It uses the Arca-swiss system. The plates are very low profile and weigh next to nothing - I leave mine permanently attached to my camera. The plates can also be made for each individual camera body or lens and so will fit perfectly and does not rely on friction to stop the plate from rotating. The only downside to the Arca-swiss system is the cost - a custom plate for your camera will cost about US$55!!!
The ballhead is also very sturdy and once locked it will not budge. It is also surprisingly light for what it can do.
Here is a review of the Acratech Ultimate Ballhead.
Love the weight of this ball head, together with a CF tripod will be best combo for those who travel a lot. But since u will be using 055Pro, the setup be very heavy still
Personally, i dun like the Arca-Swiss system, I tot of remove it from mine but cannot, so i have to stack my Stroboframe quick release mount on top of the Arca-swiss plate
may be u should try Stroboframe QR system one day, it is truely low profile, abt 1/3 the height of Arca-swiss plate, and all u need is place the plate on top of the mount and it will be locked automatically, no need to slide in and turn the screw to lock