What Type of Page is Served?

It’s just whatever the server responds with, based on its configuration. There is no “BBQ response page” or whatever, but rather simple sending of headers via PHP:

HTTP/1.1 403 Forbidden
Status: 403 Forbidden
Connection: Close

That is what the plugin sends each blocked request by default. You can examine the code on line 138 in the main plugin file. I hope this helps, let me know if I can provide any further infos.