I bought the centering vise from craft supplies. I had problems with it not drilling straight. The top hole would be aligned, but the bottom would be off center. At first I thought it was the drill press, but when I removed the vise and used a square, the drill press was vertical. The hole was off front-to-rear. Finally I took a caliper and measured the bottom plate in the vise. It was thicker in the back than it was in the front. I shimmed it a little on the front edge and now it drills perfectly straight holes.
Another tip. I have an MDF Drill press table and the vise was VERY slippery on the table so I put a thin non-skid pad under it. I actually shimmed it by putting two thicknesses of the non-skid material under the front edge. I used the thin rubber non-skid stuff you get in rolls, it is about the thickness of a sheet of cardstock.
Sharon