Okay, I made some time this afternoon to try and actually set up the equipment and make a photograph. What a novel concept!
From the time I just spent, which I'll describe in more detail below, my tl;dr is that the Feisol VH60-HA is my preferred choice, and possibly the only one I would consider with a heavy payload.
Now to the details. I used my D500 w/o grip along with Nikon's 105 AF macro combined with a 2.0TC. The total weight of this set-up was 5lb. 13 oz. The camera plate was placed in a short nodal rail so I could adjust it better for balance and that rail sat in a NiSi macro rail for fine adjustments. All of this was mounted on my Markins Q20 ballhead. The arms were mounted on my Gitzo 3541LS tripod and the Vanguard had the Markins head added to its arm. Short of close-up lenses or extension tubes, this fills the frame with a pretty small area. I am not really sure I would use this set-up for most of my work, but it seemed like it would be close to maximum payload. I had a couple of fresh flowers in a bowl and worked indoors since some of this gear will be returned. Not the same as being in the garden, but it was good enough for a casual comparison. I also had a 4 lb. counter weight on the end of each arm.
The Feisol is big and heavy and that counts for a lot. It allows for smoother movement, and the duel lever that controls the raising and lowering of the arm was quite nice. The friction can easily be adjusted, and there were no teeth to contend with. It was just pure friction. The arm, while short, was not too hard to adjust with full payload. In all, I felt this was the best arrangement for this test.
The Leofoto arm, did not really cut it for me. It is not badly constructed, but it has two design flaws that I do not care for. First, the arm has a channel that sits atop a notch, which I presume it to stop rotation. I do not find that helpful, and it is quite "sticky" so the arm does not slide easily. Second, the teeth that control the raising and lowering of the arm are a hinderance when you need to make a fine adjustment. You adjust the arm and then go to lock it and the teeth pull it down so they are aligned. Huge issue when you need to make fine adjustments. It might be fine for casual use, but I did not care to deal with these flaws. It seemed to hold the payload just fine, like the Feisol, but that may be saying more about the Gitzo then the arm.
Lastly, there is the Vanguard. I removed the pan/tilt head that came with the legs and mounted the Markins head. This is a smaller tripod than my Gitzo, and made of aluminum, so it felt a bit like getting out of a four-door full size sedan and into a compact car. The arm slides easily, but the raising and lowering mechanism is somewhat akin to the Leofoto. Under load, there is a click sound, and you almost need to remove the load from the arm before raising or lowering it. I do not know if this is a safety feature, or if there are teeth like the Leofoto, but it is a bit annoying. And despite having the counter weight, I did not find the legs to be solid with the load. Is is not a setup that I would walk away from without worrying. I would like to try this setup with a lighter load to see how it functions and if it worth keeping for light duty general use. But it would not be my first choice just for macro work with a DSLR body and lens. The Vanguard, which is made in Myanmar, requires a small amount of assembly as the pan/tilt controls need to be inserted. No big deal, but there were so many parts wrapped in foam and plastic that repackaging it if I do return it is going to require a bit of creativity.
I am sure there were flaws in my trying out these arms today, but actually shooting with them with counter weights on the arms did not feel that much different than my initial impressions when I initially unboxed them, other than the whole rig felt more stable. I am sure there are circumstances where any of them might appear better or worse, but I just don't have the time to do that kind of testing. And I am sure that there are folks who can use any of these setups and get different results. Macro work is not something I do on any regular basis, so I am evaluating this equipment with limited experience in this type of shooting.
I hope this helps others who are looking at macro arm options.
--Ken