My intuition says that, for the given spec and abilities, I would not feel bad paying 60 to 80 Euro. Add 10 Euro shipping to that, plus the games, and what I'd call a fair price is already 140 to 190 Euros. (Mind that my intuition is not yet calibrated for the current supply shortage).

And yet they sold out 40K units in a matter of a couple of hours.

So the demand is clearly there regardless of how it compares to rational alternatives.

I also found the marketing campaign had a quite good execution for something in such a niche.

All that tells you is that 40K people knew about it, wanted it, and had the disposable income to purchase it.

I bet sales slowed pretty quickly after that.

It sounds like you love the idea of it (I do too), which I think is true of a lot of failed products. I'm not saying that you should buy it or that it will fail, just that there's an interesting lesson there for creators — loving that something exists isn't enough.

If that gets you excited you should check out the Funkey S. Same open hardware and open software and included community games, but also with the ability to emulate your favorite handheld consoles.