What's the difference between "Remove ads" and "Sync Ultra"?

I'm loving Sync so far. I used the official reddit app ever since I was on Reddit. I sure was missing out.

I saw on the left bar there's two options "Remove ads" and "Sync Ultra". What's the difference? I understand ultra is a subscription that gets ad free browsing and more. However, remove ads looks to be a single purchase "add-on", i.e. no subscription. Is that the case? That would be nice down the line when sync for lemmy gets an official stable release.

There's also a price difference. Ultra is 1.99$/mo or 16.99$/yr, and remove ads is 12.99$.