Any such tools that are worth their salt have their code posted publicly, you can check it yourself. Most of it isn't some groundbreaking stuff, a lot can be stripped out by just changing registry values and other deeply-ingrained settings that would take a long time to find and edit by hand. I also don't see how "trust into Microsoft" factors in here - it's not about trust, we know there's telemetry that can't be disabled through standard settings, and I know there are features I'd like to uproot entirely (like deep OneDrive integration).