This particular weapon is essentially a scaled down minigun: a multi-barreled machine gun built to offer a dramatic fire rate without the risk of overheating, but with a significantly reduced weight and strength requirement thanks to a padded shoulder mount, on which the weapon rests. It is operated in a manner similar to the missile launcher and accepts common 10mm ammunition.
Due to its high damage per shot and good rate of fire, it is the most effective 10mm weapon in the game if you don't need the lower Strength requirement and silence of Sleepytyme (or if you don't have the Gun Runners' Arsenaladd-on). However, it can be difficult to maintain, as only other SMMGs can repair it (even with Jury Rigging), and it is extremely expensive to repair unless you have a ready supply of weapon repair kits. Alternatively if you found the 1st rank of ED-E's upgrades, repairing this gun isn't a problem.
Xbox 360 Picking up one in lesser condition than the one in your inventory may replace the one you already had with the more damaged copy. An easy way to prevent losing the SMMG in better condition is to equip it before picking up the more damaged one. Keep it equipped until you give it to ED-E or use it for something else.
PCPlayStation 3Xbox 360 While the SMMG has a defined crit damage, it has a crit multiplier of 0.