I have an RDG chuck which holds 0.2 to 13mm drills, and takes a drawbar. It is nicely finished and not massively heavy, unlike some of the cheap ones.
If using it in the headstock taper, to hold a mop for instance, there's always a chance it will come out of the taper - hence the use of a drawbar. Although I've only used it just the once, it's nice to have the option if using the chuck to hold e.g. a mop that generates radial forces, unlike a drilling operation which tends to hold the chuck in the taper with axial forces. Of course, working around the LH side of a mop may generate axial forces to push the chuck out of the spindle taper!
Similarly, a drawbar may serve to hold a chuck tightly in place when the tapers are no longer in as-new condition.
The RDG chuck arbor is relieved externally at the narrow end, and the thread is relieved internally a few mm short of the end so striking it with a knock-out bar will not damage the thread or pein the end of the taper over into the lathe spindle taper - assuming reasonable force is used!
Hope that helps the decision.
Duncan