The Gitzo 1720 does look appealing but of the reviews I've read as many don't much like it as do. It's not a fluid head for starters...
Yes, I think that users who don't like this head are disappointed that it lacks true fluid action, as you note. If not expecting fluid, I'm not sure what's not to like. With the single control for vertical and horizontal lock, it is super efficient. It operates very smoothly and it is a very rigid head. I like having a single control. Why are so few such heads available, and none of them except this Gitzo any good?
...It's fairly pricey as well...
True. But I struggled with lesser heads. This one is very satisfying as it does its job very well.
...I don't care too much for plates that utilize a pin for anti-twist, as in the Gitzo and Manfrotto designs. Arca plates are widely available in many configurations and finding one with a lip that catches the edge of the foot of the scope (for anti-twist) is simplicity itself...
What's wrong with pins? I like them fine as long as the scope foot has a hole to receive them and the pin is completely rigid (Stay away from the spring-loaded type, as found on some Manfrotto and Gitzo plates).
I also like Arca-type plates, and like you, I've had no problems with compatibility. Moreover, Arca plates can be used very smoothly in Manfrotto/Gitzo/Sirui clamps using a simple adapter--https://www.ebay.com/itm/Metal-Adapter-for-Arca-swiss-Camera-Quick-Release-Plate-to-GITZO-Tripod-Ballhead/192833703904?hash=item2ce5c8cfe0:g:LhAAAOSwd4tTwN2r--which I often do.
...I have two 3130s (same as 128) that I've modified and work brilliantly, though a bit heavier than the small Gitzo or it's replacement, but not much...Manfrotto lists the 128's weight at 2.2 lbs. I don't know where that figure comes from as I have weighed it without the arm and it's clamp and it's 25oz...
A bit heavier? The Gitzo 1720 without arm is less than half that weight (i.e. it is under 12 oz)!
Some of the arms supplied with versions of the 128 and its older equivalents were _very heavy_, so perhaps that explains the weight spec. I like the 128 well enough--it was my main head for many many years--but ironically, it was the weight of that head on my first light-weight CF tripod that started my quest for a lighter head. Before I came to the Gitzo, I tried a lot of really crappy light-weight heads. The only one that worked well enough to be tolerated (for a while) was the Manfrotto 700RC2 (Really, a _horrible_ head compared to the Gitzo). Although the 700RC2 looks like a miniature 128, it doesn't work as well. Some failings are that the fluid action can't be dialed off completely (and can get _very stiff_ in cold, depending on the individual head, with _much_ variation among units), when the tension is low the head develops play (also a problem, though less so, with the 128), and it doesn't take sliding plates.
...I haven't found a head that has better action than the 128. It also comes apart easily and can be "tuned" with different viscosity grease...
I like my Sirui VH-10X quite a bit better than the 128 even though it is in some ways less adjustable. I use the big Sirui when weight doesn't matter or is advantageous, and I have the Gitzo 1720 when I want to go light (and the RRS BH-25 on Velbon 455 with Nikon ED50 when I want to go super light). I've considered adding the Sirui VA-5 (which is Arca standard) as an in-between option, but so far I haven't found need.
Despite my argumentative stance, please know how much I appreciate your practical experience, no-nonsense evaluations, and solutions. What amazes me is that in this consumer wonderland, with so much design talent and precision manufacturing ability, is that so many heads are so bad. How to build the perfect light-weight birding head for scoping (and for cheap) is something that should have been figured out a long time ago, and we should have lots of competitive options. I don't feel that is the case.
--AP