The only paid app that I have is Moon+ Reader Pro.

I read a boatload of ebooks on my device, and this has been my ebook-reader of choice for a while. I found it to be so good that I did the IAP, and stopped using Librera Reader.

For all that matters, I am a huge supporter of FOSS apps (that’s the reason I have only one paid app lol) - but Moon+ reader Pro beats Librera in two areas - Librera is pretty slow when it tries to open a huge file, and Librera also can’t download book covers like Moon+ does.