Q. I have seen your columns about the AOGNY skin tightening machine and what it did for your jawline and under your chin. Have you tested any other models and how do they stack up? Do you use the AOGNY anywhere else besides the face? Are there other applications? —S.K., Pittsburgh A. Before I answer your question I will start with a refresher on RF skin tightening. Skin becomes loose as people age because the body produces less collagen. This leads to drooping skin and wrinkles, most obviously on the face. RF skin tightening is a clinically proven method that uses RF (radio frequency) energy t…