In the right spot they(the fluid bed designs) sound like a great unit, but just keep in mind they need a lot of water flow(more than a regular sluice). I wouldn't mind adding one to my kit, but serious lack of water around here.
The gold mat sluices are good, l use a couple of them, they like a good amount of water as well(though less than fluid bed designs). They don't like shale much, but otherwise catch gold and super quick to clean up.