That card is a true hardware-based RAID controller, meaning it has a dedicated processer & RAM onboard which will serve to take most of the job of operating the HD's off the CPU... certainly more then an Nvidia or SiL software-based controller, however that most likely won't translate into much of a performance gain in typical desktop use, not only when compared to software RAID but to a single modern HD.
It will however result in a more robust RAID configuration in any kind of computer & in a server which tends to do less transitioning quickly from read to write you would notice a significant performance gain in most cases.