As "safe" as any third party program can be, I guess.
You'll just need to ensure you're monitoring your temperatures. I've never heard of the program but, assuming it's legit, running all your cores at 100%, 100% of the time is essentially what overclocking does (although on a little lower scale).
Does the program 'control' voltage also? Usually cores are limited to the max turbo speed on one or two cores, with the remaining lagging beind a little. To get that fully stable, I would anticipate a need for increased voltages.
If you don't have a capable motherboard etc, you do run the risk of damage if that's the case.