They claim to be merging 'traditional' search results from multiple providers, explicitly calling out Oath (Yahoo) as well as Bing. So, hopefully, substantially. Realistically, somewhat.
Besides that everything I would expect from a search engine probably applies (Microsoft might get to know what I search for etc.).
But taking a little piece of cake away from Google isn't bad either.
Esp, the disable personalized results.
In their privacy section they do admit to storing identifiable information for at least 7 days (possibly more) to fight spam and improve search results. They also send user identifiable information to bing, as well, who then store it for at least 4 days. Apart from that, they use third party tools in their non-search parts which might be subject to different privacy rules than their main website.
From their app, they send information to Facebook. They use the Amazon, Google, and Microsoft as advertisment providers, if I'm not mistaken.
I encourage you to read the fine print here: https://info.ecosia.org/privacy