First of all, if you plan to buy a Canon copy, good luck finding one in stock. I've contemplated making a switch myself, to replace my Canon 50/1.2, which I have to say, is pretty much of a dog. Shameful to say, considering the cost. Canon has adjusted it multiple times, but I ind even at 5.6, it's not the sharpest lens around. Anything wider than that and it's crap. Truly a shame when you're paying for the speed. All that said, lenrentals.com has made some comments regarding the lens, which is that there are issue with the docking/calibration unit:
"Warning: We have had multiple issues with the electronics of the lens locking up after using the Sigma USB Dock and latest firmware. If you rent this lens with the dock, or want to use your own dock, please make sure you have the latest version of the Sigma Optimization Pro software installed. Older versions may cause the lens to lock up."
Take it for whatever it's worth. I'm still interested enough in dumping my 50/1.2, but will have to wait. No choice anyway. Most reputable stores have are saying 2-6 month back order. Pretty broad timeframe.