Dado sets are designed to be stacked together on an arbor. There is no interference between the teeth on each of the blades. The plates or saw bodies are meant to touch not the carbide, the carbide will break if stacked together.

The dado set is also ground so that it will give a relatively flat bottomed cut (Forrest, Amana, Freud etc will be better than HF or Avenger). Dado sets will usually include shims that allow for 0.005" adjustment to dado width.

Another consideration is material to cut. Almost all dados will rip natural wood. Very few dados will leave an acceptable cut in melamine. Of course a zero clearance insert or dado specific sled will help any set.

The cost of sharpening adds up quickly and may exceed the initial purchase price of an inexpensive dado. I wouldn't consider some dados sharp when they are new. Also, every piece should be sharpened with the set otherwise you will have uneven dado cuts.

Jerrimy