Fisher Wood Stove Insert? Hows it work?

So this popped up on FB. Hows it work? You just shove it into the firplace hole, put a border around it to seal up the face of the fireplace, and it just uses the existing flu without running any stove pipe?

Sounds crazy to me but that sure seems to be how the pictures look. Am I crazy?

Yeppers and they work just fine

because the box sits out farther in the room you get better heat off it without so much of your room air getting sucked up the chimney

smaller box than the big open fire place = better combustion

You do need some piping or a liner when doing that. Just putting a woodstove into an existing masonry chimney can have issues. The safest way is to run a liner all the way to the top of the chimney. Wood stoves or similar appliances need to have a properly engineered flue. Not doing that can cause drafting problems , excessive creosote build up or even a chimney fire.

https://www.csia.org/installing_woodstoves.html

Done right and safely , they are much more efficient than a standard fireplace.