The Marsec Minilauncher is a smaller version of Marsec Heavy Launcher. It is identical in function except that it reduces practically everything, from the size weight to halving the range and power of its munitions. It's nothing more than a trigger with a rod to stick guided missiles on.
The smaller size does allow for ultra-compact rockets. This, above everything else, makes the Minilauncher much more sought after than the Heavy Launcher. The higher ammunition capacity allows the Minilauncher to be used almost like a Megapol Auto Cannon with HE shells - with the added benefit of homing capabilities. The reduced weight and the self-guiding missiles also allow for an Agent to dual wield two of these weapons without much encumberance (other than the amount of ammunition necessary) or loss of accuracy, allowing for a discharge of massive firepower by a single soldier.
Like the Heavy Launcher, it comes with standard High Explosive and Incendiary Rockets. No one knows how you can fire the same rocket five times, but that minor detail is worth ignoring. Late availability of anti-alien gas even allows the mini-launcher to almost best the Toxigun during the final stretch against the aliens.
The lower power of the minilauncher makes it ideal for combating enemies in areas where you need to keep collateral damage down to a minimum.
The Minilauncher unfortunately has some licensing issues that need ironing out before X-COM is allowed to purchase them. This does not prohibit X-COM from seizing and using them beforehand from enemy organizations.