Did you Google Boatboard?
I thinkl it is just a marketing ploy aimed at boat owners. They call it a modified HDPE and I think the modification is the textured surface. The properties claimed are just standard for HDPE: doesn't rot, yes correct, doesn't delaminate, yes correct etc.
And $10 for 13" by 13" at 0.5" thick is about $9.50 a square foot; is that much different to standard HDPE?