For many years,the 8" Bison universal 4 jaw chuck has been my favorite. I am more likely to use square and round stock than hexagonal,so it is always on my larger lathe. I'm glad I got mine before the prices jumped so high! I must have bought 6 of them over the years as we upgraded to better lathes in the toolmaker's shop. I generally left the chuck on the lathes we sold off,back when they were much cheaper,and had differing mountings. Mine runs to .001" or better.
The Ebay one needs the other set of jaws. Being a scroll chuck,the jaws don't just flip.