Scroll down and you'll see a video.
A number of folks here use them but I have stayed away because I don't want to magnetize my knives.
My take is that once the knife gets magnetized, some of swarf from the lower grit stone will be holding onto the knife
even if you wipe it off ,causing deeper scratches than you want when moving up in stone grit. I don't have any proof as I haven't used one but it gives me a bad feeling. I do my best not to cross contaminate my stones either.
While the EP is much easier to learn than free handing (by a bunch) there is a small learning curve- light,consistant pressure as well as a consistently holding the knife on the blade table.
When Ben Dale does it in his videos it looks easy because he has done thousands of knives. After a couple dozen I picked it up so anyone can