The stick works great on calves and lower leg, and it is effective, but I prefer the Tigertail, which is like a foam roller on a stick. Look around for it on Google. It's usually $30, but I got mine for $15. The advantages of the Tigertail is that you can use it on your upper leg about as well as a foam roller, except you don't have to lay on it and you can reach those hard to get spots. The stick doesn't do as well on the upper leg.
I would definitely invest in one, but keep in mind that it is mainly a preventative measure. It's good for muscle knots, but if you have a tendon injury, then that isn't going to fix it up right away. It will help prevent tendon injuries, though, by loosening up your muscles and creating less strain on the tendons where they attach to the bone. It's a great tool for injury prevention and recovery.