"Open source" but the backend is paywalled. Paywalling any crowdsourced web service is plain unacceptable.
Edit: turns out my privacy concerns were unfounded, as the paywall is completely client side. It can therefore also be edited out with a single line of code.
As noted on the payment page at the bottom, the license key is used in one request to the server to validate it, but is then never sent to the server again. Your userID and submissions are never sent with your license key so they cannot be linked.
The extension is also not fully paywalled. You can still request free access using the button at the bottom of the page, and I hope many people take this option! I don't want everyone to pay
