If you're looking to clamp up large table tops, you're going to be into huge money for the type you linked to or the many different k-body style others have recommended. Don't get me wrong, I have many k-body clamps but none longer than 36". But back when I started out, i bought a handful of pony bar clamps and bought some black pipe to make several long lengths. I still use them to this day.
Having a large assembly table will help you keep them flat. Otherwise, there are many jig tables you can cobble together to help you with that.