We used to use the trigger top in holsters on our duty belt. The thing is that trigger tops are made for precision aiming of the canister, and as you indicated, once used, were cycled out and replaced. That way, we could tell if the officers were using them on people or not.
Only way to get a new can was from the station. If someone complained about it being used, the officer in question had to produce his can, and show it hadn't been fired.
In a holster on your belt they are fine. If you ever get hit with it, you will know it. We were using Capstun. Man, that stuff is bad. for most defensive uses, a civilian wants a spray instead of a stream. A stream requires precise aim, and is designed to only hit the target. In order to become accurate, you have to practice, and practice canisters cost money. You do not want to practice with a live canister. Even walking around where the stuff has been sprayed and you risk getting a whiff. which is enough.
Spray will hit the intended target, and may hit bystanders as well. In most defensive situations, you should take the risk, and get yourself to safety. Only reason to use stream is to avoid hitting anyone else when deployed, and you have to be accurate.
Best way to carry is a belt holster. I would never trust it in my pocket.
Those dates are probably date of manufacture. Check their website for expiration.