That's not so clear. Police are aware that tasers don't leave marks -- i.e., much harder to get a jury to sympathisze than with photos of bruises and broken bones. Video of a taser attack looks a lot less horrifying to a jury than the Rodney King video. The company that makes tasers also helps fight any lawsuits against them quite aggressively.

And if you're within billy club range the person just might be able to land a blow back on you (not relevant of course when they are tasing already handcuffed and prone individuals).

It's not at all clear that the number of tasings is equal to or less than what the number of clubbings would be.