No, not all tinctures are the same strength. They will be graded with ratios like 1:1, 1:5, etc.
I would start with a single drop and wait a day or two before increasing. Japanese knotweed is very strong. And we couldn't use it. There are alternatives. Buhner advises to build up to a dose you tolerate and everyone has a difference tolerance. He recommends dosing till you experience a "side effect" then going back to the previous dose.