when crafting stuff that makes multiples.. aka not armor or weps
main hand gives +1 +2 ect
off hand instead of +1 2 ect you get more of tthe crafted item like 6-8 instead of 4 for +1 2 respectivly
From what I've seen so far, main hand tools tend to have more +Craftsmanship than +Magic Craftsmanship. Offhand tools tend to have more +Magic Craftsmanship than +Craftsmanship. The trouble is, the way they add a second type of main hand tool + the way they tier the optimum ranks for tools, you frequently end up with a main hand tool that's better for all around synthesis where you're only selecting a different tool if you're aiming for increased quantity from HQ instead of +1/2/3 etc.
Not really, GLD (Goldsmith) main hand for brass nugget = more, offhand for brass nugget = +1/+2/+3, I have had +1 Nugget before, but I just dumped the offhand altogether. The only time when you're worried about +1/+2/+3 is the final product, and it seems both tools will produce + when HQ. No reason to waste an inv slot to carry an offhand tool around.