None whatsoever. Two however are 1/2". The 1/4" by 15" round was chosen so Laurie could easily lift it. I'm not there now to hold a ruler against it, but I've never noticed any issues as I watch fat move around on it, stovetop. Leveling the gas range is the dominant issue, not warping.
I deliberately did not buy the griddle with a fat moat. I never create enough fat to be an issue, and there's always paper towels for the outliers. Don't walk away, one could imagine how a grease fire could start here.
The 1/2" is an incremental improvement over 1/4", with 3/8" perhaps a happy compromise. Various vendors on Amazon sell work-alikes thinner than 1/4", and defend their economical choice with comments about how slight the marginal improvement is with thickness. But hey, do I cook on a Weber or a Komodo Kamado? The marginal advantage may vary with the application, but it's there.