I use the same house rules and yeah, the tricky part comes with the fact that it doubles all the weapon attack rolls, so... sneak attack would also need that 6 instead of 1d6, for instance. At the moment we just play it like normal, but use the right side roll as the max. The right side is important unless you want to do redundant math, since the default crit system will apply your modifiers and bonuses (the values that are not doubled by crits) to the left side . So.. we roll, we see what we get on the left side.... And on the right side it's just pure dice rolls, no modifiers, so we just change that in our head to the max number. It's not optimal ofc, but at least it works. We used the left side first until we noticed the detail about the modifiers.
