I get it, you would trust yourself if you said that, but it doesn't really matter whether you say that or not, what counts for your ongoing credibility if you will preface every future blog post with, whether you got special access, a special deal, sponsorship, or the fact that you didn't get any of those things.

You're a reviewer. This is how reviewers stay credible. If you don't disclose your relationship with the thing or company you're reviewing, I'm probably better off assuming you're paid.

And if your NDA says you can't write that in your preface, then logically, it is impossible to write a credible review in the first place.