I installed one on a 7K trailer I used to have for towing my one ton K-5 because @ 7K GVW, it was maxed out.
It made a huge difference and made towing easy.
Upgraded to a 10K trailer recently but kept the sway control simply cause it works.
A properly loaded trailer shouldn't really ever be a problem but having run these systems for a couple years now, I'll probably always run em.