How viable is the hippopotamus defense? Clearly the defense is not viable in top level chess for classical time controls. Roughly at what rating is it viable to have the hippopotamus defense as your primary black defense?
It depends on the players and how black continues after whites moves.
For me, I find it easy to beat players using it for black.
That might speak more to their lack of experience than the opening.  But then you dont find many high rated players using it so there is no conclusive proof.