Hi Mike J 17,
The SI fin is a great fin!  It comes with all of our Cruiser longboards except for the Merlin and Plantain that come with the MP design shown on the paper diagram earlier in the thread. As of today, the Super HP is not yet available and is in the testing phase.  The HP series fin is only supplied with the HP1 "High Performance" single fin board. 
I wouldn't put the SI if I didn't feel confident that it was a superior fin design.