WRT the ones on eBay, I have no experience with them. If the threads inside the draw tube properly fit 5C collets, then the only question is length. If too long, you can cut it off. If too short, you may be able to shorten the spacer/thrust bearing. As a rule of thumb, the proper length is when with between 1/2 and 2/3 of the threads engaged, a collet is tight on a work piece of the matching nominal diameter.
As a side note, never use a handwheel type draw tube or draw bar that has been adjusted for length by sliding the hand wheel up the tube or bar, leaving part of it sticking out. Sooner or later, you will forget and hurt your left hand by trying to hit the wheel to release the collet.