What do you use for initial idea evaluation?

[muffin38man]

I'm curious about your experiences. I consistently read that people recommend using Google Keyword Planner, Facebook Ads Manager, or various SEO research tools to get an initial idea about the potential size of an idea or topic. This makes sense to me, and I've tried it many times. However, most of the topics I'm researching either don't have any data or the data is obviously incorrect (e.g. super niche topics have millions of results). In any case, I don't find it reliable and can't really use it at all.

Since this approach has been so consistently recommended, I want to sanity check my experience and see if anyone else feels the same way. If so, what do you use instead?