6% is insignificant compared to the 200% returns here. Anyway they could sell for a nominal amount maybe?

I don't see why it being public would matter: the whole point is that this should be legal since the owner is only airbnbing it for 60 days.

That's 6% every two months, so you're going to be paying 36% of the value of the apartment every year. For an apartment that costs, say, half a million, that's 180,000 euros a year in taxes. I mean, if you're renting the flat for 15,000 euros a month (instead of the 1000 it would actually fetch), it might work.