Mag Lights and the old Kel-Lights have been used as impact weapons by LEO's for years.. they are highly effective... much more so than an ASP....
an ASP has certain advantages for LEO's.. the primary is availability.. it is always with you.. PR-24's and Straight Sticks tend to get left in the car alot because they get in the way, and difficult to manuever with, and are a general pain in the hind part when it comes to taking it off, putting it on, taking it off, and putting it on again, over and over... then when you really need it, its in the car..
a pr-24 or straight stick however typically deliver MUCH more blunt force trauma than a collapsible.. this is the primary reason you have seen an upstart of "conventional" weight and length collapsibles such as the winchester baton and the wide diameter monadnocks (a compromise between capability and comfort/size)
a C or D cell flashlight comes much closer to replicating the blow delivered by a conventional baton than a collapsible does... the additional weight allows for deeper penetration and greater "fluid shock wave" transfer when delivering strikes as taught in the PPCT, ASP, or Monadnock systems...
personally, i have never had a problem dropping someone with my 21" ASP upon first strike, but that isnt always the case for other officers.. i have bent 2 collapsibles however to the extent that they were non repairable...
a 5 C cell mag light is my personal favorite for an "improvised" impact weapon...