Both actions restrict visitor access to your store, but they work differently:
Block — The visitor is shown an access-denied message and cannot proceed. They know they have been stopped.
Redirect — The visitor is silently sent to a different URL of your choice (for example, your homepage, a custom landing page, or an external site). They are not shown an error message.
Which should you use?
Redirect is generally the better choice for country or region-based restrictions, especially if you want to direct visitors to a localized version of your site. Block is better for specific IP addresses or known bad actors where you want hard access denial.