Just to through my 2 cents in, I have an "A" machine that has done a great job for me. I have had the carvetight chuck for a while - I guess it's time to install it. If you are comfortable working mechanical problems, I would not hesitate to purchase it new. All of the bugs on the "A" model can be found here on the forum. Believe me, the people here on the forum can get you past any difficulties you may encounter.
A couple of items to really consider adding - The probe with the Pattern Editor, Centerline, and Conforming Vectors. These will add greatly to your experience creating projects.