Don't forget highway interdiction operations that require certain knife builds. A lot of cops don't need much but some do. Speaking from experience it might not be a bad idea to get a small flat plain edge fixed blade to wear behind your magazine pouch for rough work and purely self defense reasons if you're on the ground with a bad guy mounted on top of you beating the crap out of you and you can't get to your pistol, taser, or baton. As a blunt force tool, you won't need it. The end cap of your baton works much better. If you're smart you'll keep a window breaking hammer in your car. The carbide tip sucks on the end of a knife, it's always poking you and wearing holes in your pants or shirt. I'd suggest a serrated edge folding knife with a good steel like H1. You might need it to cut straps, zip ties, tires, airbag compartments, etc. You'll also need to pry covers off of the center console, break open glove compartments, fuse box lids, interior air filter covers, dashboard covers, screw covers, kick panels, etc. where your fixed blade will see the most abuse. Your fixed blade should be the go to for shimming a car window to unlock the door, shimming open frozen car windows if it gets cold where you're at, prying open a house window quietly, etc. Sure, your dept will issue tools but you'll find quickly the less tools you carry on you the better. Most guys I work with, though, make it just fine with a leatherman, a crap pocket knife, and a small crowbar tossed in the trunk along with a roadside interdiction kit that has grommet pries, wrenches, etc. in them.
In the end, I suggest getting something that you like the looks of to start out with, is comfortable to carry and use, and fits your budget. Once you're on the job for a bit you'll find what's important in your tool kit and what isn't. Each person has their own techniques for whatever it is they do. Most cops honestly don't truly need more than a good leatherman. That's the truth if it. The rest is just tactical hoopla or are on some level of the knife hobby or they've been told from the academy forward that a knife should be carried by LEOs. I am kind of different in respect to what I do. I search A LOT OF stuff and cut open MANY boxes and pallet straps and auger into many pallets, usually without the luxury of a good tool kit because the tool kits are shared and for whatever reason most of the useful tools keep winding up "lost." I've also been stuck on the side of the road in the middle of nowhere and all I have is a small set of tools to cut, pry, and peel all kinds of crap.
My duty carry for right now is a spyderco mule team fixed blade because it's small, light, nimble, very well made, easily accessible and quick to return to the sheath, and controllable. It's not too heavy, not too light, and with a set of Halpern scales fits my hand extremely well. It's also cheap enough to actually use the crap out of it. For folders, I've owned probably 20 or so, not many but not few, and most any folder does pretty much the same as another, in reality, as long as the folder comes from a good manufacturer anywhere in the world. But my main three right now are the spyderco military, the ZT 0560, and Spyderco ppt, in that order. They're all great knives for the price. In all reality I could get by with an ontario rat folding knife because I'm capable of sharpening my own knives when I need to.
Hope this helps.
