For under 20 dollars you have to wonder about quality - I will say - wonder no more. These are, as far as I can tell, great tires. If you put them on suitable rims, you will convert a mountain bike into a bike that does everything well - they won't roll as fast as 120psi road tires, or 100 psi 26" slicks, but they roll fast enough for riding on the street, and have some other advantages.
One - super comfortable. Two - the inverted ridges help you out a bit on gravelly sandy areas. Three - you can abuse them more than high pressure tires.
Would buy again, although I am tempted by the slick-er slicks that GEAX makes. GEAX is the ATB division of Vittoria, if memory serves.