[...]Currently the Gen2 Piranha has metric-only version and a standard-only version.You are correct in the fact that the box end only truly works as a box on the largest size but have since kept it in that configuration as the box allows for a user to apply more torque without the tool flexing as much. This isn't readily apparent, and has been a discussion here since Day 1. With these things in mind, we will be introducing a new Piranha in the near future that has a standard open end and a metric closed end. There will be some more features added as well with this new design.
Seems the Gen3 could be the one to get.