As for implant materials, here's what Eppley says about them:
"Facial implants come in two basic materials, silicone (which is by far the most commonly used) and medpor. (porous polyethylene) Each material has its own advantages and disadvantages, neither facial implant material is perfect. Regardless of the implant’s composition, they are all placed in a subperiosteal position right next to the bone. Most of the time, the implant is secured to the bone by small screws so there is no chance of shifting or implant migration."
https://www.eppleyplasticsurgery.com/cosmetic-facial-implants/If you're considering mandibular angle augmentation, go chat with him and let us know what he says.
If you want to steer clear of the silicone, perhaps the medpor would be a valid option.
I would much rather an implant than HA paste.