Very little is known about these small medieval and renaissance crossbows and there are very few in existence, but all were loaded with a screw jack in the grip and usually had a top trigger and were often highly decorated.
They are also known as assassins crossbows, though the low impact energy really counts this out, so we suspect they were rich men's ‘executive toys’ rather than weapons.
The bow has a high poundage at 220lb, but the short draw length means this cannot be translated into a powerful shot. However they are great fun.
You can see one in operation here
You can see Tod and Matt from Schola Gladiatoria chatting about these here