Now I know why I like Tamron!
I have the 17-35 and I quite like it. Not sure why it's a disappointment for you Africa.
The dirty little secret is the 3rd party lenses manufactueres have to work harder, builddecent quality, and charge a lower price to compete with the name brand lenses.
Not too say that the high end "L" lenses don't earn their keep. But we'd all like to be drinking the highest quality French Bordeaux, but most of us end up settling for a decent priced Californian Cabernet Sauvignon.
So, for those who earn their living by the lens, the high end is definitley justifiable.
But for the cash strapped amateur and semi-pro, these 3rd party lenses are a god send!
Now if I could just afford one of those expensive French reds on a regular basis!