The effect actually raises all stats for the equipped servant’s Buster card. However, the Star generation and NP gain bonuses are effectively useless, because Buster cards have low values for both anyway. Which makes the effect only useful for its damage increase.
Stats
Min
Max
HP
0
0
ATK
500
2000
Effect
Normal
Increase Buster Card effectiveness by 25%
Max Limit
Increase Buster Card effectiveness by 30%
How to use
There are also other CEs that give a combination of an Buster effectiveness buff and another effect (such as critical damage, or NP charge) which might be more effective in some situations. Such as: Victor from the Moon, First Sunrise, Kaleido Ruby, Joint Recital
Use with servants that just wish for lots of firepower with their Buster cards, even better if their NP is also a Buster type. Most of Berserker servants work well with this CE.