My rule on grills is that, if it fits, it fits. I once bought an adjustable grill to put in my Brinkmann but I found that it fits perfectly into the top of aluminum catering pans so I use that for my Hibachi style cooking.
One thing I would hesitate on with any other grill in the BGE is cooking at high temps. If you're gunning to run at 600F or whatever, I'd stick with that heavy duty cast iron grill that comes with the BGE.
That's my $.02USD anyway . . .