While I don't personally own this lens, I have borrowed it off of a friend and it is indeed a fine lens. Great bang for your buck and my friends who do own it continue to take fantastic macros with it.
As for the discussion about third party lenses, I have no issues with them myself. I have owned several lenses from Sigma (30mm f1.4) and Tamron (17-50, 28-75) and I have loved them all. For comparison sake, I did also own Canon's equivalent 24-70 f2.8 L series lens. While it was definitely sharper than Tamron's 28-75, I had to crop images to 100% to really notice. For all intents and purposes the images from both cameras were great and useable. I sold the Canon 24-70 f2.8
L because it was way too heavy for me to lug around. Yes, I'm a weakling. But in photography, there really is no point in buying or keeping a lens if it's just going to sit in your camera bag, which is what ended up happening to my more expensive Canon 24-70L. I used the sale of that lens to buy 3 new lenses
Also, Sigma and Tamron do develop lenses with their version of Ultra Sonic focusing motors. Definitely great value those lenses.