If the spraying/spreading of the stuff only works for a short while, why bother? Concrete walks keep out vegetation better than brick-they are certainly not as pretty-but if you believe beauty is function...
The rest of my driveway is concrete, but cracks form and grass and weeds grow up.
So, I can either pour a brand new driveway, pull weeds out by hand, or spray weed killer a couple times a year.
I go for the cheap and non-labor intensive method.