Been in law enforcement for 30+ years...
Back in 68, we were told to go out and buy a nightstick, as it might come in handy. No instruction, no technique; whack em' on the head if they give you trouble. Lots of broken nightsticks and heads.
Later on, my department brought in this English guy who had a nightstick "course" consisting of a single technique; a two-handed forward thrust to the solar plexus. Needless to say, this guy has been lost in obscurity.
Then, the side-handle baton became the rage; new to law enforcement, but old hat to us MA types who knew a bit about Okinawan-derived Karate.
As stated above, the problem was complexity. However, current training theory, as espoused by PPCT ( I'm a qualified instructor ) is that complexity is a problem not only because cops are too lazy to train, ( well....) but from a physiological standpoint. Under high
stress, with the pulse above 150 or so, our ability to perform complex actions gets badly degraded. So, PPCT, and now other systems, use simple, gross-body-movement techniques that can be used under stress.
We currently use the ASP; I dont find it better one way or another as a weapon. It is more portable, and that's a plus- the officer
doesn't have to fuss with keeping a solid stick in the car, remembering to take it with him each time he exits, and having the damn thing dangling from his belt, along with all the other bits we have to carry!
I have a bit of background in Filipino techniques; but using these highly effective practices in a law enforcement context will likely get you fired or indicted, unless it's a "deadly force" situation.