Slab said..
What would you normally surf on those waves? Slate is more a smaller wave machine? Looks like it held well though...good surfing!
Actually the parallel rails give a lot of stability at speed: you get the rail curvature of a longer board.
What is tricky is if you try to make tight turns in the hollow sections: then the wide tail may be problematic to sink properly on the rail to get some hold, and the rail-to-rail is harder: slower, and may "squirrell" in the transition. But holding the rail on the trim line on a steep face is actually enjoyable as the rail is very straight, no wobbling like with curved outlines that ask to be always turning.
Also chop & bumps hit harder.
This on my limited experience in some overhead sessions (not as big as the pics here!)...