Interesting, but Central Authority are notorious for changing or breaking their own rules to get what they want.
I'd be sceptical of any claim that 'Eminent domain' or 'tax free land' will be honored. Well, it will be for a little while anyway.
But... is the fee and costs worth it if it still might be taken from you, a group or even no one in particular?
Very true, but completely unavoidable as a potentiality if we're talking about a piece of land on current-timeline Earth. Organized Crime Syndicates (governments) literally claim to own ALL of it. They are far less likely to break/change the rules that actively protect their own investments & "wealth."
But it has been so far, for hundreds of years. It's not nearly as good an option of having a private non-state island built or something, but it is by far the best option to "own land." If one is going to start a land-based project of any kind, why not use the very best, most Lawful options available.
There's a reason billionaires do everything through trusts and other Lawful means that most aren't familiar with.
It's better than nothing. Though, Billionaires have the money to defend themselves against governments in courts.
Hell, the average citizen can't even beat an oil company these days and eminent domain is not even supposed to pertain to them.