I haven't tied the crystalline specifically, but I have tried other glossy canvases that say no varnish required. IMHO this is BS. You might be able to stretch the canvas without cracking (and you might not). But even so, the surface is too delicate to survive without a protective varnish unless it's going to be displayed behind glass. Best to spray and be safe.
I've also found that these canvases look better with after spraying (to me), the varnish evens out the "sparkle" that these glossy canvases have when uncoated.