Yes, as philipma1957 said, I own one and so it is free - but my experience with a powered hub was not good - of course the spacing was too close so I could only plug in 3 Antminer U2/U2+ and the device dropped so much voltage that I had to feed it with 5.75 Volts to get 4.25 out - so as you say the hub needs to be capable of supplying current in excess of the USB2 spec and if you look on ebay they seldom give that information and maybe you have other problems if you use a USB3 hub.

The points made by alh are a valid criticism.  I had a cable to hand for a hard drive that took a normal male USB connector so that wasn't a problem for me and I used one of those Buck converters with a variable output one can buy from China or Hong Kong on ebay as it was before I found the Vinsic device (which as I suggested is quite nice for powering a number of PIs).