For those that don't do CQB, you can't be loading mags using your rifle behind the firing line, because mags (loaded or unloaded) can't be inserted into a rifle/pistol until the command to load is given only when shooting and on the firing line. It's that safety thing, and nobody likes to hear guns being charged behind them, or heaven forbid, the bolt slamming closed....
Mind you, you could reload while firing, but the amount of time is so short you'd be hard pressed to do it. Not really an issue if you're doing Service Rifle where they'll give you time to bomb up mags, and you're on the firing line so using the rifle isn't a problem.
I plan to try out the CZ next year for CQB and maybe Service Rifle, so I'm interested too in finding if there's mag chargers for the CZ. With the NATO/Stanag .223 mags, preloading your ammo on CF surplus plastic stripper clips the night before and using the CF issued plastic mag charger makes bombing up mags simple and fast, either behind or on the firing line. The guys that don't fire .223 are at a major disadvantage for time, and then rushing to reload makes it hard to calm down for the next shooting stage.