Well it depends how you look at it. It definitely adds to network traffic and CPU load. But IFRAME content and javascript-injected IFRAME are both loaded asynch

Well it depends how you look at it. It definitely adds to network traffic and CPU load. But IFRAME content and javascript-injected IFRAME are both loaded asynchronously. Browsers are pretty good in progressive rendering of page content these days. So user should see the main page first and then it starts loading these additional resources. So no big deal IMHO. The button should not degrade user experience during page loading.