I would say a dull or a honed insert is preferred. Personally, I use an edge of a used insert. For better finishes from a carbide face mills, make sure there is proper seating of the inserts. You can use the compressed air to clean the machine tool. You can also cover the pockets with a good blast to ensure that all the dirt and debris are removed and the insert has a clean pocket to seat against.
Make sure that the spindle face and the socket are clean and well maintained. The adapter should be straight and well fitted. The cutter back face and diameter reference should be running concentrically.
In brief, this is what you should be keen on; matching inserts, cleanliness, undamaged body parts, honed edges where applicable, straight reference feature and tooling. You may also dial in the edges, I works!