I have one and have posted about it. Try searching on "Beseler Slide King" for some previous threads.
The quality is good, but it's designed for use in a large auditorium, and it can be hard to find lenses short enough to project a normal sized image in a smaller room. I think the shortest I've seen is 6.5". It wouldn't be hard to adapt other lenses.
Also, you may not find carriers that correspond to available contemporary mounts, so you will likely be cutting your own slide mounts or adapting a carrier to work with mounts you can get.
Also, advancing the frames is a strictly manual operation where you insert the slide in the carrier, shove it into place, take out the previous slide and insert a new one, slide the carrier over, change slides again, etc.
That said, once you sort out all the details, projected medium format slides from modern color films are stunning.