Duller blades are way more unsafe. Having a very sharp blade is much safer. Just hold your scrote taught with one hand and run the blade lightly across the hairs but not the skin on your first go to shorten the hairs and rinse the blade then go across the skin lightly.

Dull blades lead to applying more pressure to make the same cut as a sharp blade. More pressure means more chance of a deeper cut if you slip.