I saw this too! Unfortunately, HS/STF and B Spec guys won't be running this which seems to be where most 2 owners race. Unless there's some guys building H Prod/STL cars? Derrick?
I have used Cusco diffs in other models of Mazdas and they work great. Installation is a transmission rebuild as you have to take the whole thing apart to get to the diff and setup the lash on the diff with new bearings.
I am not building an HP Prod or STL car out of a 2 anytime soon.