I’ve had my sonic 11m for about 5 months, and have no seam problems yet, even though it has been tumbled in the surf many times. I have found the wind range quite large and have been out in 30 knots, gusting to 35. It starts to behave badly in those conditions however it is still quite useable. And yes the leading edge must be pumped up hard otherwise it is a pig. I don’t have a pressure gauge so I squeeze about 6 inches in from the end on the leading edge. If my fingers can touch, not enough pressure.
I have also found that the kite flies better when the rear lines are connected to the forward attachment point on the trailing edge. It steers a lot quicker and has a better feel at the bar. It depowers quicker (less bar travel needed) however it feels as though there is slightly less bottom end.
On the negative side I have had problems since new with one bladder that had a manufacturing fault and have not been able to purchase a new one.
It appears that you can’t get parts for them and it’s not because of the retailers..

..... Also I had the webbing break between the chicken loop and cleat. When this happened the safety disengaged as it got pulled through the chicken loop/cleat cover. Lucky it landed in the surf and didn’t hit anyone on the beach.
Would I buy the same kite again??............not sure at the moment……