The real question is always "but how good is it at killing non-cancer cells?" A bullet fired from a gun would be great at killing cancer cells too. Although in this case it seems like it's just an alternative to surgery, rather than a cancer cure? Just a way of vibrating cells in a certain location to death? Does anybody who actually understands medicine know if this is a great breakthrough or not?
It means, at worst, don't go outside or be in bright sun-lit spaces, but also, we can shine a flashlight on where the cancer is to kill it. Even if it weren't very selective (which could be adjusted with other targeting molecules), light-trigged theraputics are easy to understand the propagation of.