I was so glad to see infinity for lemmy. I used infinity for reddit and that had a ui that both looked good and was intuitive. I was super excited to see that there was now a fork of it for use with lemmy.
No you don't have to pay at all actually. In fact people can choose to pay for something they love that works better than half the Lemmy apps I have already tried. I will pay for something that works.
Open source doesn't always mean you are any more safe either. I feel like this community thinks it knows more about security than it actually does.