Why would you spend money on PWM controlled pumps and then use voltage control with them.
I'd rather have them hardware controlled than hooked to a motherboard header. It's much simpler in my opinion. I'll run my fans, for example, at different speeds depending on more than just my systems temp (as long as they're in an acceptable range). Mood, headset, company to list a few. A single rpm:temp software profile wouldn't do.
The FC5 happens to be the only controller I already own.