At the start of a new game it's very useful, because it frees you from the annoying need of slowly chopping a lot of trees at the beginning, cause now you'll cut them trees like you were picking flowers.
Over the time of use your manually works are getting slower, because the effect is wearing off, down to normal speed.
I'd prefer if the effect would reach below normal speed, even to cannot craft, cut trees or mine manually, even move anymore if you are too exhausted until you had some rest and your stamina has regenerated again.
(-> Stamina-Scale indicator:
[0%(nothing goes)...<slower than normal>..100%...<faster than normal>...300%]
something like this, with some kind of logarithmic behaviour (later addon could craft/assemble power drinks of some kind)...)
But at the moment there is no regeneration, only the effect is wearing off down to normal speed.
So it's just a help for the start at very beginning of the game.
And I don't know if it's a useful thing to carry a mod a whole gamelife within that's just used for the very first 3...5 minutes.
