Aside from just flow, you need substantial head -- their flow chart shows that their smallest 500kw turbine needs at a minimum 1,200gpm and ~60ft head through t

Aside from just flow, you need substantial head -- their flow chart shows that their smallest 500kw turbine needs at a minimum 1,200gpm and ~60ft head through the turbine, so you'd need a river with much more than that so you're not fully destroying the ecosystem. That really, really restricts the possible locations.