I'll chime in since nobody else is.
KSC/KWA Makes some of the best pistol replicas in almost every pistol model. They are somewhat spendy (usually $125-$200 each), but the tradeoff is you can get3,500 pellets for about $15 bucks. And a couple cans of green gas for $10/each.
They run off of green gas (or a mix of propane and lubricant), are gas blowback to cycle the slide and provide a little recoil, and you can do all of your mag changes, etc. Very realistic for training purposes.
Glock replicas are really hard to come by due to a trademark infringement filed by Glock. But KWA/KSC makes 1911s, Sigs, M9, H&K USP, etc.
KWA/KSC PTP (Proffesional Training Pistol) Models are very accurate replicas both in size and operation. They're designed to be used exactly as you want: as an identical training pistol. Decockers, etc. The Sig M226 even has the double-action first round like its RS counterpart.
As a Cadet with the local SO, we have used airsoft for training, and it certainly changes the dynamics of a scenario. Things are different when the subject(s) can shoot back
One thing I have noticed is that some replicas aren't perfect, so fitting into RS holsters may require some modification (read: dremmel/sanding) to get a good fit. At least I had to with a Blackhawk! Level 2 Drop Leg platform. I know the standard belt holsters have more success since there's less holster to get the replica into.
Disclaimer: READ THE USERS GUIDE FOR YOUR AIRSOFT REPLICAS AND ALWAYS OBEY APPLICABLE LAWS. Airsoft can be dangerous, so please take the proper safety equipment should be used to insure the safety of all trainees involved. Eye protection at minimum, and full face masks are recommended.