In spring, when they spawn, they are not so good to eat. The scales are rough, unlike those of a plaice, which are smooth. You will find flounders in the sand and mud of every river estuary around the Welsh coast. They even run up river well into the freshwater reaches whenever heavy rains brings the river into a muddy spate.
Worms are an ideal bait for flounders, although big ones do include fish in their diet.