We have the gas blowback KWA "professional training solutions" M4s and AKs.

Several advantages IMO - weight and feel is identical to your real gun. Magazines hold both the gas and BBs, and that's 40 BBs, not 400 BBs, which means like real life, you have to change magazines. No electric gun or paintball 400 round "hollywood mag" BS.

Your picking up the same weapon you use on the gun range, the balance, the operation, etc. is identical.

If your out in the woods for a couple days, all you need is cans of gas and BBs, no electricity needed to charge batteries which is nice cause in almost 40 years, I still haven't found an electric plug in a tree in the woods yet.

For FOF inside structures, we use the gas Glock airsofts. Same thing, they feel and operate just like a standard Glock, fit the same holsters, etc.

Only thing we found was last weekend at a ground fighting/fighting for your gun class we held was that contact shots with the airsoft Glocks were hit and miss. What I mean by that is sometimes they would shoot just a smidge out of battery and sometimes they would not.

We use the Glock airsoft in SHTF pistol class where the last day is working clearing problems in a 2 story actual house with stairs, T intersections and a bunch of "problems" like that. First it's force on target, then you go against role players inside the house

The gas M4s we have mainly used in the past on jungle lane scenarios at rifle and NV training classes. Finding small camoflaged targets near a trail you walk and engaging them. Due to the particular angles on where we set up the lanes on our range, it's safer to use airsoft for that. Since the objective of that particular part of that class is FINDING the targets, it works perfectly for that.