I don't know how powerful. It will fit a half sheet. The door is a little less than a foot high and the interior obviously is smaller. I wasn't being "I made timing measurements" exact by saying "almost as fast" - think "almost as fast for my purposes". It takes about five-ten minutes to preheat and my old toaster oven took minutes, not tens of seconds. I don't remember how many. It's just a big enough improvement over a full height oven that we use it a lot more, and don't bother with a toaster oven.

You also can toast just about anything in it under the broiler.