I have this moment when I have to use Youtube on my phone for some reason (such as a tutorial for how to fix something), and get blasted with 3 ads for a 1 minute video. I would never use it for long periods without an ad blocker.
Also, there's an option to enable SponsorBlock, which can automatically skip over ads, introductions, etc. that are part of the original video.
Vanced and Firefox's addons are two of the main things keeping me off of iOS.
But ultimately, you can either examine the binary yourself or else trust them.
One point of note is that it does not automatically update. Whether you install it directly or use the manager app, there is always some manual process involved in updates. (The manager just notifies you when there is an update available.)