I like working with light PG ply, except for one thing – since it has a wood core instead of MDF, it warps like crazy (at least here in Colorado – YMMV, of course).
My light proofgrade came warped. Keeping it under stacks of heavy materials didn’t help. Needed tons of hold down pins, then glue and clamps to get it to work Even then, I wasn’t totally satisfied with its bowed appearance.
I have had luck flattening boards with a flat board and weights on top when they are sprayed with alcohol first. Allows the grain to stretch (or some other physics thang).