You can opt out of training.

If you don't believe checking the opt-out box actually opts you out, then this sentence could be said about literally any provider.

Yes but grok has the literal track record of our of the box uploading your whole codebase, secrets included to a remote box.

If I recall correctly that was a bug, not malicious intent. Hanlon's razor makes me presume that's likely.

Maybe I am biased, but the person in control of that specific company is by far the most untrustworthy.

All providers are equally trustworthy :)