My question is how strong is the material? What does it have for compressive strength? Tensile strength? Torsional stiffness? etc. It is probably like Starboard, which is also an artificial lumber, but isn't recommended for structurally significant use. The fact that it floats tends to lead me to believe it is probably a form of Polyethylene or a foamed plastic product, like some forms of starboard, and may have the same problems with lack of strength.
I am a retired carpenter / cabinet maker and have used the stuff.
I used it for a sub-jamb for half circle window. It is made and used for exterior trim like soffetts.
It has almost no structural strength.
If you get a small cutoff it seems pretty strong. A longer piece feels like a wet noodle.
As a support beam most anything is stiff if it is deep enough but I would want to load it to failure before trusting it. Does it deflect with constant load? Does heat make a difference?
The problem with these new materials is that they can have failure properties that are significatly different from traditional materials.
As for a core material i used 3/4 inch and it was sold as boards so there would be a lot of seams.
I just looked up the material on their website and notice that they sell trim and deck material.
The deck material may be stronger.