Any size is legal.
A paddle may be of any size, shape or weight as long as it is flat and rigid and of even thickness. I notice that the thickest sponge thickness the Spin Technologies has is 2.5mm. When you add the measurement of the 2.5mm sponge to the measurement of the rubber attached to the sponge, the thickness is at the 4.0mm maximum. Yes, it is now legal to reglue your rubber as long as you use ITTF-approved glue. The reason sited for the original ban was the health hazard involved in inhaling some components of glue.