The way I see it, there's a time and space for both. "side products" require much more upfront time investment than "side projects" (market research, competition evaluation etc). It depends what one is looking for at the moment: is it a potential business? (->side product) or exposure to a new technology to help you grow as a developer? (->side project).
I agree. I am not a great fan of side products because that is a whole other goal. That is all about making money rather than learning more. Its just not me.
If you structure it well, you can have your cake and eat it. I enjoy many frivolous "side projects" that are merely for research or to learn a technology, but where possible I try and plan for that "play" to then serve as the basis or inspiration for a product or service I can offer as well (at the worst, a fun side project could turn into an interesting piece of content marketing, a prime piece of your résumé, or even something like a class or an e-book).
The way I see it, there's a time and space for both. "side products" require much more upfront time investment than "side projects" (market research, competition evaluation etc). It depends what one is looking for at the moment: is it a potential business? (->side product) or exposure to a new technology to help you grow as a developer? (->side project).