About 10years ago I saw polystyrene compatible polyester for the first time on a french site. My local polymer shop told me this is not possible and that it probably was some other type of resin.
Now my local shop released a new solvent free polyester resin themselves.
I think the intent of the resin is to allow tooling like large molds to be made from EPS.
It was not a clear or optically brightened resin so boards have a bit of a vintage brown tint, It smelled like PE resin after being catalyzed and until it cured. Costwise it was about halfway in between PE and epoxy. We probably should have pigmented it white for our 1 PCF (.88 actual) EPS surfboards. It did take a blue tint really nice.
After tearing one board apart I found out that there was exotherm or solvent damage around the fin plugs using this resin. Since it was board #2 there was probably some operator errors committed while using the resin too, like perhaps too big of holes for the plugs or not doing them in two pours.