i'm using a 6P with a A19 and P91 for my M4A1 and i'm having no problems with it. the vibration you're getting from an AEG does nothing compared to a real rifle's recoil. now dropping the gun light first or running into a tree or soemthing light first in the dark (hasent happend to me.knock on wood) it may or may not survive, surefire or even cheaper brands.
the 6/9P is good for distant and also the colour is more natural to look at so you or the person's eye wont hurt as much looking at it at a certain distance unless you are using a M6 or something else as bright. you cant leave the light on to long or it'll be very hot. i left mine on for a few mins and i started to see white smoke from the lens or the around the lens area. anorthing thing with incans is that it will go dim after a few mins of use, which is one reason why i'm concidering using an LED instead.
i forgot what that models name was with the L4 weapon mount. anyhow, an LED like the L4 will be regulated so you'll have a constant brightness for about 2 hours..? it'll turn on faster and an LED hurts more to look at between 10-15 feet, which depending on the rules you play for night games its close enough to stun the person you're pointing at to shoot or mercy him/her. you get a bit more flood to the light which means you'll lose out to distance compared to incans and you may or may not get an LED with a donut hole. also with the flood you might blind yourself from the sidespill if you're playing in a wooded area with bushes.
heck, buy a U2 (multibrightness) or A2 (best of both, incan and LED! good size light as well) and that L4 weapon mount. the A2 with red (saves night vision, also batteries) or white LED is good for walking around or finding/changing stuff in at night and if you hear someone coming at a distance you blast them with 50 Lumens of regulated light. when you're going for the kill you blind them with the L4. i'm hoping to get a A2 for myself as a sidelight just for using it during airsoft. until then my U2, L2 or HDS will have to do. speaking of those lights, mutiple brightness lights are a good tool for this sport. i was thinking of using the U2 for the M4A1 but the light will alway turn on low before quickly jumping to high or whatever level you set it to. its alittle big but i just love the quick brightness level access like the L2, unlike the HDS i have to click 100 times before getting the right level but the HDS is freaking bright and i love the size. small, light and bright which is also good cause you might be carrying alot of gear on you.
oh crap i'm blabbing too much. sorry making you read so much