This is the first heavy weapon acquired (during the escape from Lazarus Station), and remains quite useful in many situations. Its reasonably high damage, coupled with high accuracy and rate of fire make it a great all-round heavy weapon.
The M-100 Grenade Launcher deals splash damage, making it a good choice against groups of small targets.
The grenades tend to follow the target, similar to the ML-77's rockets but to a lesser degree.
It appears the M-100 had a Codex entry, however it was cut from the final game.
The grenades that the M-100 shoots look and behave more like rockets.
Although the weapon's description makes mention that the Blood Pack's vorcha troops utilize the M-100 as a favored weapon, no Blood Pack troops encountered by Commander Shepard's team are seen wielding the weapon.