Psshh. I already have two of these, one on each side of my foregrip, so after the SHTF, when clearing the local hospital while raiding for supplies, coming to those pesky T intersections, I can look both ways befor proceeding.
I use a 40mm M203 grenade launcher for this app myself, the dust messes up my jet black cammies, but sometimes you just have to deal with these things. That's why I carry martinis in my canteen, it eases the pain.
Hey it's better the putting a 90deg bend in your barrel plus you can aim!!!!
The Germans tried the bent barrel thing in WW2. The Ferdinand self propelled gun didnt have a machine gun mounted on it . but did have a small vision hatch on each side. the russians would climb on the gun to place explosives and the bent barreled gun was to shoot them off. Didnt work to well since they couldnt aim. Looks like they needed this sight.