I went diving in Zihua in September last year (2020). The diving was perfectly mediocre. I love diving, so I'm glad I went and if you are in the area, you might as well go. Things were very quiet at the time. It was just the captain, DM, and myself. We did see other dive boats at some of the more popular sites at the time.
I went with Zihuatanejo Dive Center, just around the corner from the pier. I chose it based on convenience. The DM was friendly, although his English was only so-so. I don't speak Spanish and it wasn't an issue, but I'm comfortable communicating in gestures and broken Spanish and English. His English was good enough to communicate everything you need to know about the dive and safety. The owner had excellent English. The equipment was well maintained and air seemed fine. I really enjoyed the laid back and personal touch. When returning I'll go back there even if it is the less convenient option.