After my post in August last year I had to call out an engineer (via Samsung) as I just couldn't get the grill to work properly.
He didn't find a fault, but I wasn't charged for the callout because I think he recognised that the instructions aren't clear. What now works for me is a) to remove the dual partition before grilling and b) try to open the door as little as possible during grilling, as the grill will automatically cut out every time the door is opened. It heats up again quickly but it's not an efficient way to work.
Following those instructions I can now use the grill pretty successfully, although I agree it's not great if you can't open the door often. Grilling fish fingers (the thing we grill most regularly) takes no longer than on my previous oven, and they're cooked evenly.
The one thing I can't remember, from the visit, is whether the G1 or the G2 setting is better. He told me one worked better than the other but I forgot almost immediately afterwards. Maybe someone here can help? If not, try experimenting.
What works for me may not work for you, but I hope this helps, and that maybe someone official can jump in and confirm.
