I still don't think I agree, sorry. You might want to make something as good as possible so people are more likely to pay for it, but all the time it's not launched nobody is paying for it at all.

Not really, I know a bunch of companies that would fail lots on this list but are making millions.

For a side project you'd probably be better off putting much more basic things like 'does it work on mobile', 'do the email addresses listed actually work', 'is robots.txt still set to disallow google' and 'have you actually gone through a whole order yet' on there. Seriously.

"..this is a good check list if it's a 'side company'"

That's actually a better term! It makes a difference whether you are building the side project as a creative hobby (to develop new skills etc.) or in the hopes of turning it into a startup.

back in the day we used to call that a "lifestyle business"

Eh, not really. A lifestyle business is your main source of income. It's not a side project. It's just not a startup because there is no massive growth expectation.