The barrier to use a taser is too low. It might not be a lethal weapon in waste majority of cases, but neither is a batton. However, more consideration is used with the use of a batton and officers are much more likely to get in trouble for using a batton needlessly.
We have a few videos where a suspect is outright electrocuted to the point they can no longer function, even though it wouldn't been necessary to take it as far, and the officers, if unlucky, are at most reprimanded. Had a batton been used to the same effect the officers would be facing a judge.
Tasing, as an action, shouldn't be taken lightly just because it's considered as non-lethal.
I can't see why they tased him for the first time, but I do understand if they want to tase someone reaching out for a gun, even if just to secure it. I suppose the guy attempted to secure his gun as a result of training. However it wouldn't have led to that had they not tased him for the first time.