Any of the big agents and their title companies such as Magic Vacation are well used to doing this. They essentially withhold the tax from the seller to cover the tax, so the buyer has no worries, and if instructed (for a fee) will put the seller in touch with an expert to claim it back (cost about $500 to the seller- this does not hold up the process- a seller can fill in the paperwork themselves).
Bottom line there is no problem buying from an international seller if you use one of the main agents and title companies, and the advantage is it looks like it would not be taken ROFR.
As to it taking more time- maybe maybe not, depends on country. For example with the UK (Hague convention country), they can go to a UK notary with no apostille from the US embassy required for Florida- should not take any more time than a US seller going to a notary. I just bought a contract from a US seller and it took them weeks to send the paperwork back as they sat on it whereas a motivated UK seller could have had it back within days.
If however, you were buying
DVC in California, the UK notary could notarise, but then I think it has to be sent to the US embassy for the apostille which will delay it a bit.
In summary, I would have no qualms whatsoever buying from a foreign seller, for Florida property, particularly from foreign sellers based in places like UK, Australia or Canada. In fact due to the lack of ROFR, even waiting for a short while longer (which you shouldn't technically have to) could save you lots of time compared to it being ROFR'd.