Unlike Anemic Agility and Vile Acceleration, Frail Momentum gives the same amount of fire rate as the non-corrupt equivalent, Shotgun Spazz. As such, Frail Momentum should only be used in conjunction with Shotgun Spazz in builds aiming to maximize fire rate.
The negative damage boost is additive with other damage boosting mods such as Point Blank. Combining a maxed Point Blank (+90% damage) with Frail Momentum will result in a total damage bonus of +75%.
The actual net damage loss when combined with a maxed Point Blank is 7.9%.