We always have 2 12' slings on the hook, and try to use 2 for most picks. It doesn't take that much longer to place the slings, and the picks are more controlled. We do this whether using shackles or hooks. We don't have a steadfast rule about always suing 2 hooks. When we are picking wood, we use one sling and one shackle or hook most times.
Spider legs are an invaluable tool, and will be more prevalent in crane work in the next few years. Everything new takes a while to catch on. Imagine when guys went from cables and chains to synthetic slings. Those old salty dogs must've laughed for days at the new blood using fancy polyester slings. Now look at us, could you imagine moving a 10,000T load with chains?! How about using chains everyday in a tree, be pretty tired at days end wouldn't you?
We have to keep our minds open and clear and not knock new techniques so quickly. Especially if we haven't tried them, and only going off looks.