Performance is not quite live up to the SATA 3 full price, but far exceeds the performance of SATA 2 motherboard. However this card being PCIe 1x it is better to stick to a single drive, although it allows to connect two. I did not test RAID 1 or 0, but comments on a forum indicates that it does not work on Mac.
In short, if you want to connect a SATA 3 SSD Mac Pro cheaply this card is for you. Certainly it will tweak the internal wiring (especially for food), but it works.