I really do not know very much, I bought $10 cheap "Omega" tool last year but never try it, it works on grafting branches with same diameter, Sharpness of blade is a key of success, My fig tree is not fully wake up yet so its branch is very hard, this tool is not able to do a clean cut now, it might work well when branches softer later, This cheap Omega tools come with low quality of blades so be prepare to buy new blades.
I think I would prefer using grafting knife, However, My hand skill is so poor, I should train my hand by peeling potatoes/apples skin using knife.