I received my griddle last week. It is a nice hefty piece of iron. The casting is crap. It makes Lodge look like Griswold. Lots of flaws.
I decided to grand it down before seasoning and using it for the first time. Hit it with an 80 grit flap wheel on my angle grinder. I suspect an 80 grit on an orbital sander may have worked too, maybe better. 120 on my palm sander did not work.
At any rate, grinding it down really helped smooth it out.
I then seasoned it with Flax oil on the kettle, then cooked with peanut oil. brushed off after cook and seasoned with flax again. It worked well and was nonstick.
Will post the cook in a separate thread.