I’m using this all the time myself. There is no login to YouTube required and it supports adding subscriptions and doing everything important you can do on YouTube.
And the best part is no ads whatsoever.
Since they are integrating a web browser in the app
are they, though? I thought they just grab whatever data Invidious API fetches and display it with their method of choice, similar to how mobile clients for Invidious and Piped work. PlasmaTube manages to do similar thing without becoming a single purpose web browser.
FreeTube uses their own API (Local API) on top of Invidious’ API. you can choose whichever, and the other will be the fallback that’s used.