I'm considering buying a Le Creuset square grill pan and panini set. I know that they are supposed to work great on a gas range, but I'm needing to use it on a smoothtop. Has anyone with a smoothtop used one of these and if so were you satisfied with its performance? They appear to be flat on the bottom. Also, an employee at William Sonoma said to treat them like cast iron and to only use a wire brush and water, but the instructions say to use mild soap and water with a sponge. I'd be interested in hearing what any of you have to say on the subject, especially after reading the cast iron post...