I have one of these backs and no, it isn't a ground glass back. you load the sheet film into special sheet holders and then put the holders into the back. then you pull the dark slide. the next step is to lower the holder to the film plane, then take the photo, lift the holder and put the slide again. it's a bit slow, but it works well. you don't need a ground glass as the sheet sits in the same position as the film. so focussing is as usual.
yes, it only makes sense if you want single sheets. but there is plenty of film that doesn't exist as roll film. so it does make sense.
I would be willing to sell mine, I'm in germany. the snag for the moment is the following: the back is in my french home. I am confined in germany under strict rules. no way to visit france yet. but that will be over in 2 or 3 months...