This won't help you take out Reapers. And it's probably not such a good choice against Cerberus, either. At least, not if you want them to stay dead after you shoot them.
Because this? Is the best Nerf gun ever. It's Commander Shepard's favorite Nerf gun on the Citadel. It's a Nerf gun painstakingly handmade to look like it's right out of the Mass Effect series. If the Alliance could get away with Nerf guns, instead of the hot metal kind? They'd use these.
It's from Etsy designer Viktor Graves, who has a whole bunch of amazingly detailed, mostly harmless, fully functional replica weapons available. But this one is the best. Because Mass Effect.
And if foam just isn't an effective enough weapon against your nemesis, there's always the Super Soaker watergun edition. Which is pretty damn cool too.