I have used it and its not bad there is no auto feature it just allows you to change bios settings without having to reboot. Just make sure you remember what the settings are so you can put them in your bios after.
Programs like these are Windows based overclocking utilities. It's much better to learn to use the BIOS.
Having an ASRock X58 Extreme and having also overclocked my D0 920 to a 24/7 stable 4GHz, and if your mobo BIOS supports it, I can honestly say that you are better off using the EZ OC/OC Tweaker presets in the BIOS or manually setting the oc in the BIOS.
OC Tune is cute but not very reliable or stable, better to use the the BIOS.
I prefer the tool more for giving me accurate system temps, voltages, and fan speeds in windows. I do 95% of my overclocking via the bios... but the slight tweaks are a nice option to have in windows. I'm able to run my 920 at 22 multiplier (turbo) from the default 20 set in the bios. It's also nice to verify your settings within windows, and since it's provided by asrock, the readings are accurate (no random 134c bogus readings like I saw with a 3rd party app).
I think of it as an app that is a complimentary tool, not necessarily a replacement for overclocking via the bios.
I did find that it will blue screen the system or make it freeze up completely if you make too drastic a change in timings via windows. I never felt comfortable changing setting more than a few percentage points... if I got too greedy it would lock the system up. Like I said, I do 95% of the overclocking changes via the bios... but tweaking a setting here or there is nice in windows (i.e. voltages, etc). I wouldn't jack up the FSB by 30mhz via windows and expect the system to not crash.