I think there's a couple of folks here who use them, the more common term is a discada cooker. The FireDisc looks like a combination burner/stand/discada. Look in the food threads for the chicken spiedini post from over the weekend, that was done in a discada, I think.
I don't have any experience with it but just judging by the pic it resembles a unit that Rectec sells as their RT-G540 Matador. If that's accurate, you might get some additional feedback from that forum or elsewhere. https://www.recteq.com/RT-G450-Matador-Gas-Wok-Cooker_2
They were originally made from a plow disk that cuts the sod before the plow turns it over, by welding a patch in the hole in the centre. Also from the disks on a disc harrow. Now there are companies that make them just for the purpose of cooking on them. They have quite a following in certain areas. Lots of sites like “thesmokering.com” and “rokslide.com” have discada forums.
A flat top griddle and a discada are really different cookers. A flat top has a pretty even heat distribution, a discada has a more concentrated heat source around the lowest point in the cooking surface. You can also shallow fry in a discada without any extra pots, you'd need at least a fry pan on a flat top to achieve the same effect.