I saw this and wondered whether anyone takes periscopes to CQB? We've all seen the mirror-gum-knife thing, would a cheap periscope (/w BB shield ) be unreasonable for airsoft?
I dont see why not, you see all sorts of stuff hanging of of peoples kit, if you feel it could have been useful in the past and may need it in the future then go for it..
I have a silencer-mounted mirror on my MP7 sometimes. It's rounded, so you just have to stick the tip of your gun around the corner and it works rather well. But as Elts said, mostly The Mall is too fast paced for me to warrant using it.