Since the Tamron partly better, and this is also confirmed by some tests than the C *** s is 24-70 MK1, one suspects at a significantly lower price of course disadvantages, and there is.
The quality control of Tamron is not optimal and besides aperture problems have very biele copies Focus problems. I therefore advise the lens to test after purchase to Focus difficulties and optionally send back for adjustment.
After the adjustment, however, you have a very very good lens in hand, which is narrowly surpassed only by the C *** n 24-70 MK2. That costs but also about twice as much.
Who very good sharpness, focus speed and accuracy (after adjustment!) And processing at a more than fair price will, and the possible sending of adjustment, etc. is not afraid of being in good hands with the Tamron.
But if you want just a prefektes product without complications, which is on top of that minimal sharper (barely perceptible) and is ready for it to pay twice as much, but you should pick up the Canon.