I have used my grapple extensively. Mainly for clearing debris, cleaning up chain sawed trees, digging up trees and moving them, clearing areas of brush and trees up to 6" diameter, etc. I have a strong opinion a narrow one will do all of that great. And one thumb works just fine. It will hold anything I grab easily. Mine is 48" and heavy duty steel, 1/2 " thick. A wider one will also do most everything but dig. If you just need to scoop up debris, a 60" or greater works fine. But if you need to dig up trees, or uproot them, which I do a lot, a narrow one is far superior. My analogy is that if you manually dig up a shrub, you use a pointed shovel, not a wide snow shovel. Same principal. And for grabbing debris, the width doesn't really matter. Limbs and such tend to interlock with each other so it's not necessary to support the whole pile. It still gets picked up.
So if I do any uprooting at all, I would make it 48" wide with heavier steel, one thumb and cylinder. Advantages are that it saves weight over a wider one allowing for more lift capacity and breakout force, more simple, cheaper, and it will out dig a wider one hands down. And to me, it still works just as good as a wider one to scoop up debris. The thumb really doesn't do that much. It just clamps down on limbs as you transport them. For big rocks the thumb does even less. the weight of the rock keeps it in the grapple. A single thumb is plenty to hold it in place. I see no advantage of two thumbs unless you have a grapple 6 feet wide or bigger. But then, you lose the digging ability.
