Hate to say it but a Chromebook is absolutely no different than putting information into an Android tablet, they're all going to be looked at by somebody. Google definitely looks at all information going across their networks. Do they mine it and sell the compiled data, yes they do. Do they Protect Your Personal Data, yes, they obey the law.
Should you trust Google? No, Google itself says you should not trust anybody over the Internet and that
you have no expectation of privacy in Internet communications. Somebody is going over your posted stuff all the time.
Chromebooks allow you to work offline now, have for the past 8 months now.
Chromebooks are still developing, as is Android -- shame is that they both lack a "declared plan" so nobody really knows what they are going to wind up being ...
Android is going to fragment some over the next year or so, and some of the variants are going to begin to smell more like real operating systems.