How effective is endermologie in reducing cellulite and how long do results usually last?

Very temporary. Endermologie works by creating a small amount of swelling under the skin. This 'plumps' the skin up, thus improving the appearance of cellulite. The results rarely last more than a day.
Harmess, temporary. Endermologie is a vacuum type massage. It has almost no risk, but any effects are probably very short-lived.