Electrolysis is the only officially recognized permanent hair removal methodology in the world. However, this procedure is painfully slow, and sometimes, each hair needs to be treated more than once to fully kill it. Unlike laser, however, electrolysis in the hands of a competent practitioner guarantees that a hair will be killed. Moreover, electrolysis can treat all types of hair, including fine hair and blonde hair, both of which laser hair removal cannot kill.
For darker skinner people, electrolysis can cause hyperpigmentation, In fact, I got that side effect in the middle of my eyebrow area and the skin remained dark for 1-2 years. I had thermolysis done in that area by a very experienced electrologist who did not realize that this side effect was possible. Blend is somewhat safer than thermolysis, but it seems like hyperpigmentation and skin damage is less likely with blend. With a good electrologist, neither blend nor thermolysis can cause side effects. There are several types of thermolysis treatments too.