I liked Pettson because he's awesome and invents things. I think he's like a physical version of the guy who writes a bunch scripts that together are able to do all his work.

Findus is more of experimenter. He comes up with an idea about something, and ends up following that idea so that it gets tested. He isn't a systematic, scientific experimenter though, since he's a cat.

I also liked all the little animals. To contrast that with the Moomin stories, I only saw it on TV, but it was immediately obvious that they were very austere and very Finnish, even though of course, the author is a Finland-Swede. It's good stuff, but can be, not scary, but something adjacent, to watch as a child. It might be worth it since it allows you to understand these characters in this very austere, isolated environment.