I challenge anyone to produce video evidence that between two wood spearguns with identical stocks, shafts and bands, the roller speargun has more power ie. more penetration at the same range than the conventional version. By identical band power I mean for example: conventional 2 x 16mm and roller "1" x 16mm.
My premise is that personal anecdotes are just that, but physics don't lie. If you take a roller speargun powered as described above and turn it on its side, you'll see the same exact configuration as the conventional speargun, with one band stacked on top of the other. More so the bottom anchoring point doesn't always reach quite as far back as the last tab on the shaft, so band stretch is actually less. The pulley being the only differentiating factor, are divers supposed to believe that it somehow magically amplifies the stored energy of the bands?!
Nor do I believe that the roller's band powering the shaft longer is a factor. The dispersion of the band's energy over the top and bottom of the speargun may or may not result in less recoil. But that's nothing that a conventional speargun with the right mass can't do. Even if it were true, it's by far offset by the tedious loading procedure. But I digress, this is about one claim "more power" so show me the money.