It doesn't help because it gives people a feeling that they're already doing something big. That way they deprioritise the environment in their head and do less things that actually matter.

Instead, just refusing an unnecessary work trip or something once a year helps a lot more than using ecosia.

There's a problem with "feelgood as a service" when the problem is so big it needs drastic measures. It gives people the impression that there is a quick fix. Whoop, I just changed my default browser, great, I've done something to solve climate change! But still eating 300g of meat every day, meh.

That's what I object with with ecosia. They talk of "saving the planet" on their website. But on a global scale it basically does nothing.