A regional plan works in every country on the list: cross a border — data simply keeps working. No need to buy a plan for each country.
A regional plan’s price per gigabyte is usually higher than a single country’s: it pays for several networks at once. If you’re going to one country, the better deal is that country’s plan.
You can buy a plan in advance: it waits up to 180 days for activation, and the validity period starts with the first connection to a network. The QR code arrives right after payment.