Will faja ruin BBL hip results?

The type of compression garment and the length of wear is plastic surgeon dependent.  Follow your plastic surgeon's post-operative guidelines as he/she knows the extent of your surgery and how well you are healing.
I do not recommend a garment or faja that is extremely tight over the buttocks. I typically ask patients to use adjustable garments with multiple bands so that tension can be adjusted and the areas of liposuction are less likely to get a fluid collection.   The garments typically do not cover the buttocks.  The key here is the size and the ability to tighten the garment, not the brand or make.  In my practice, the compression garments are provided as part of the BBL post op package.

Dear dollxo,
I understand your concern. It is best that you consult your plastic surgeon regarding post operative care and management (i.e including massage techniques and timing) specific to your case. Your surgeon knows your condition well and has preferences on when and what to use for faster healing and recovery. Post operative care and management depends on the type of surgery performed and the technique used during surgery among other factors.It is best, however, that you follow your plastic surgeon's advice on post operative care management for a smooth and faster healing and recovery.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery