I bought cheap belts (not DeWalt) and they were ok for rough work but not nice to use; they had a large 'bump' over the seam. Anyone who has used cheap belts will know this too well! Every time the joint of the belt runs under the sole of the sander it jumps slightly off the work piece just like running over something in your car. Makes sanding more unpleasant than it needs to be and more tiresome.
Anyway, gave up on the cheapo ones and bought these DeWalt, a lot dearer but worth it. MUCH nicer to use, no bump felt through the sander!