I recently purchased the Gitzo 2720. I used it for about an hour in the backyard with my 80 mm Swarovski scope and Velbon tripod. I bought the head because I really hate separate pan and tilt locks and really liked the idea of a single lock for both.
I love the single pan/tilt lock although it takes more turning than I would like to lock it down completely. I use the scope with one hand on the handle and one on the lock wheel and it is very intuitive and easy. No where near as fiddley as heads with separate tilt/pan locks. I think the head is worth it for this feature alone and it makes the scope very easy to use and point.
The QR plate is long so balance is easy to adjust and it locks very securely and has a separate pin to be sure it does not slide off. Scope mounting is therefore excellent and probably the best I have used.
The head locks very precisely where it is aimed with no play or drift once locked. From this perspective, this is the best lightweight head I have tried.
The movement of the head is smooth but I have tried other heads that are more fluid. This might be an issue for videographers. When set at an intermediate drag setting, the head moves smoothly and keeps the scope pointed where you aim it when you take your hands off. I find even the lowest drag setting a little stiff but it does help prevent the scope from flopping at any drag setting.
As far as stability from vibration goes, I think this head does a good job for an 80 mm scope. However, I think my Manfrotto 701RC2 was better. Although I have not tried it, I would imagine the smaller Gitzo 1720 would be inadequate for this size scope. I also do not think the 2720 would be the first choice for digiscopers although I plan to use it for that purpose.
Overall I really like the convenience of the single pan/tilt lock. The head is smooth and stable. I think it is a good choice for any spotting scope. Hard core digiscopers with heavy rigs might want something heavier and more stable. If you prefer separate pan/tilt locks I do not think there is any reason to buy this head. The comparable weight Manfrotto's are perhaps more fluid and very slightly more stable. Just be prepared to be flipping locks all the time!
Mike
Newark, DE
Henry
Although you have bought the head, for any others considering buying the Gizto Birdwatching head, see the link to a Youtube video i recently completed, it graphically shows the features,
http://www.youtube.com/watch?v=wQE8046Z01M
Regards
Paul