I have three lenses in this range, the Canon 70-200 f4 IS, the Canon 70-300IS and this.The Canon non-L lens and Tamron are more or less identical for sharpness with a tiny victory for the Canon, although it's more expensive.
Very good value, lens barrel nice and wide for easy gripping, good stabilisation, although does jar in the viewfinder when it comes on, fairly sharp at 70-200mm; Good warranty
Average to poor sharpness between 200-300mm, turns the opposite way from Canon lenses; Makes an odd click/crunch on mounting; I wouldn't want to get it wet