I love FOSS but I too use Sync. Used it on Reddit for the better part of a decade and it's made Lemmy more accessible for me and also some friends.
In the end if people are happy to pay for a client, which then builds the membership of Lemmy communities - what's the big fucking deal? I'm very happy to be here and very happy to continue supporting a dev that does fantastic work.
Also using Sync. The thing is, I'm sick and tired of being told how I should need to interact with something. This isn't an argument against FOSS at all btw. I also pay a non-FOSS one-man-shop for my RSS reader.
My main thing is I want to bend the web to my preferences instead of the other way around. If devs like this are going out of their way to do that I'm going to make it worth their while.
Shit, I even pay the guy who keeps the Chumby servers alive. Just so I can have a flash-baswd Star Trek themed clock face active on my nightstand.