The only problem I see with them is with there being a hole under the pan, in the rain, the water is going to run somewhere and if it can soak through to that hole, there's going to be erosion and you're going to lose the soil from other parts of the bed, exposing the trap and clogging up the space under the pan so it won't drop clean.
I've been using nothing but am thinking of switching to polyfil and a trappers cap as a 1-2 punch.