Not so much messy depending on the type of ammunition you buy. Most Airsoft pistols and rifles have different size Barrels that allow for Multiple Types of BB's. Anything ranging from 6mm plastic pellets, 6mm Steel Pellets, or even 6mm paint filled rounds. So when its comes to messes yea you can have one if you buy paint rounds for whatever Airsoft you buy.
I personally am a James Bond fan and happen to have Airsoft replicas of a Whalther PPK and PP9.
Though to fire rounds Airsofts can vary ofcourse. Whether you have to manually cock the gun by pulling the slide back and then getting one shot off then have to cock again. Or there are ones that use compressed air like a super soaker in which you have to pump them and get a few shots out of them. Then the others types are ones mentioned earlier require CO2 tanks. Becareful when handling Airsofts that use CO2 and have Gas blow backs or you may end up with an injured thumb without having the proper hand placement posture on certain firearms.
As for saftey issues all of them have there quarks. When done properly yea Airsofts can be safe to fire upon other willing and properly attired persons for the sake of whatever film your making. But if you have alam dv i dont see why you would feel the need to fire the weapons with live ammo other then for blood spatter effects with 6mm red paint filled bb's.
Aside from airsoft guns with gas blow back you not going to get a hollywood style slide action of pistols , for example, in a real semi automatic fire style. Where every time you pull the trigger the slide pulls the next BB into the barrel.
But then again common sense has to come into play when dealing with firing Actual Airsoft guns.
I've managed to ramble on but need less to say for 20$ you can get a Whalther P99 that can pull the slide , release the weighted clip etc... you can even buy after market silencers for airsoft pistols like i did for my James Bond effect. Its a nice over all Prop looks and feels like the real thing. A lot of fun can be had for movies espcially with the slide lock switch as well.
I found it on amazon.com and its decked out with a lot of tactical features which are detachable ofcourse if you want a stock looking pistol. It doesnt require CO2 for it has a manual cocking slide and comes with a lil starter pack of 200 yellow plastic BB'shttp://www.amazon.com/exec/obidos/tg/detail/-/B00019T4AC/ref=pd_sim_sg_4/103-8533025-4039044?%5Fencoding=UTF8&v=glance