I can't find many good sources but made many observations.

The punch dagger which is often laughed at, is actually a very good weapon. It's used with the shield just like a gladius and you can get far more force using the handle bar because it doesn't actually rely on grip strength. The extensions protect the wrist quiet well, and you can twist it with a lot of force too which you notice as soon as you've got the point stuck in something. Can you slash with it? With the H shaped grip, when you hammer fist with it, the side becomes the pommel, and with a blade which doesn't weight much there's little point swinging it, the power comes from the elbow either way. When you use it with a shield it's rondelo like qualities become more obvious. When wearing chain mail or heavy gloves that thin handle makes more sense. I wouldn't recommend it for fencing, but like the gladius I think it's a side sword exclusively for use with a shield