I think the issue becomes how much do you sacrifice for smoke bomb. I think it could be useful on the Ark, as you are alone and it could set up abackstab. But at lvls 10 to 20, is it worth sacrificing critical hit buffs, which can allow you to do damage in the hundreds when combined with sneak attack. I'm trying out the smoke bomb build for the first time, but so far, it doesn't seem to stun much to make it worth all the skill points needed to employ it.