It looks like a nice size stable plateform. I'd make a few suggestions to make it more cross marketable.
1) removeable plugs to seal the front and rear of the compartment when a speargun isn't inside.
2) change the handle and small d-rings on the sides to something more substancial to hold, tie or clip onto.
These would make the plateform more useful for surface support during skills training. I could foresee it holding a fold up anchor, extra weights, slates, snorkels, spare masks or a variety of other items.
3) LED lighting for surface visibility with some light aimed at the dive flag. (for night use)
While you may have designed it for hunters the most successful products can crossover into other target groups.
Of course pricing is always a factor.
