This quad equalizer is free in the literal sense: no subscription, no trial that expires, no feature locked behind a paywall.
There is no account to create and no usage limit — you can reload the page and use it as many times as you like. The project carries no ads or affiliate links either, so the free version and the only version are the same thing.
Because the tool runs entirely in your browser, there's no server cost per user to process your audio — that's a big part of why it can stay free with no catch. Check the Disclosure page for a plain statement of how the project is (and isn't) funded.