I use Kavita and I'm really happy with it. I understand your reservations about the subscription, but I'm not subscribed to the premium features because I don't need them either.
The PDF reader on it is okay, I think. I really prefer reading PDF files. I usually convert my PDF comics to cbz. But yeah, I like Kavita because it's easy and convenient.
I don't know what they're talking about. Elon takes twitter very seriously, he uses it every waking hour of the day.