I recently acquired one of these used having previously owned a Canon 24-70L (had to sell it last year)
My use is primarily landscapes 99% of the time, so we're talking f/8 and beyond and manual focusing. I'm satisfied with the sharpness but the Canon most definitely had the edge when it comes to contrast and colours. I'm not too keen on the Tamron's focus ring as it doesn't feel very precise, again the Canon trumps it with superior handling.
I think the AF speed in the Tamron lens is more than adequate for my needs, it seems to get a bad rep in this respect but I have no issue with it. I'm also satisfied with its performance when shooting wide open, no complaints
I'm going to stick with it for now, bought for £199 used
I'll most likely be shooting with the Canon 24-105L next year I reckon, need the extra reach and IS is a bonus