1) Yes. But they, like all supplements, are progress enhancers. If you're not already on a good training and diet plan, making progress, don't bother.
Generally recommended first thing in the morning, and 4-6 hours later, if needed.
2) No. As long as you stick to the recommended dosage. Taking 12mg of ephedrine 2-3x a day is not going to make your heart explode. Taking double or triple doses won't speed up your progress, but will put you at risk.