Well, I do love these lil' guys, but it took me a while to realize that they are responsible for killing much of the plant life in one of my favorite tanks.
I had hoped my Betta coccinas would eat them, which is why I introduced them to that tank. They are prolific breeders, so even if the coccinas are eating a few Gammarus, they are not keeping the numbers down adequately. Since adding a couple of adult ancistrus to that tank, it does seem to me that the numbers are less.
In another tank, I have an angelfish that I feed scuds to. He likes them, and manages to catch most of the ones I put into that tank for him to eat. I have a great fear of a Gammarus "take over" happening in that tank, too. It is 2 feet deep & 4 feet long, so maintenance is sort of difficult. I take a rather hands off approach to care.
Getting ready to add another omnivore- a Cichlid - to that tank w/ a reportedly strong hunting character. There are also several ancistrus in this tank as well. So hopefully I can avoid having the plants stripped in that tank, should enough Gammarus survive to breed in there as well.