You can use the search function and find 30 other threads asking about what cpu fan to use on an sk-7.
Specifically about the SF II w/ CoolMod, I have one. First the good news. It's detachable from the fan, so if you don't like it you don't have to use it.
The Cool Mod has 4 long wires (one from each LED). This is in addition to the 3 wires for the SF II. They make a big mess but with some tape and/ or bread ties or something and running them behind the mobo tray you can get them halfway hidden and under control. You unplug your LED wires for the front of the case, and plug these in instead, or use an adapter and plug them straight into the PSU.
Once hooked up and with the wires finally hidden as much as possible, the CoolMod's 2 blue LED's stay lit all the time, and when the Harddrive is used the 2 red ones light up. It seemed pretty neat but the colors were a lot different than the colors on my other LED fans, so I took it back off.
That's my experience. It only costs an extra $4 or something, so if you decide you don't like it, no big deal.