Speed Chucks is a nickname given to a Nunchaku design where the handles are about 8 inches (shorter than normal) while the chain is about 8 inches long also (longer than normal). because of this they are more flexible and as such are said to be faster, hence the name, however Prochucks (more or less the opposite) are fast, in fact possibly faster, however this all depends on the user.
Flexible - meaning can wrap around the body easier
Potentially more fluid with practise (think of it like speed-rope or pro-stick)
Short Handles meaning little extrudes from hands - less to catch on other objects
Long chain can be awkward for some moves, notably wrist spins
Short handles can be difficult to catch at first due to smaller target