I want to point out that in the change log it was mentioned:

"With the addition of crit it seemed that higher crit skewed the results in favor of having Gauss Barrel active; it means that higher iLvl will result in quite a large gap between not having Gauss Barrel active and having it active."

So if this is true then the effectiveness of Gauss Barrel mostly relies on gear. So experience and practicality may vary based on the individual.

tldr; if you lack in gear Gauss Barrel might only be useful as an opener, if you are very geared you may benefit from trying to keep Gauss Barrel up often.