I'm not even sure what side effects "display: none" would have here.. But that's beside the point. The point of prerendering is to to deliver an instant "swap"

I'm not even sure what side effects "display: none" would have here.. But that's beside the point. The point of prerendering is to to deliver an instant "swap" of the prerendered tab when the user navigates to that page - think of it as a hidden tab, which gets swapped in for your current one. As a result, the render is "instant". With iframe.. you obviously don't get that.