As far as side effects go, it's a low dose stimulant. Some people experience very significant stimulation for the first few days, but it passes quickly while appetite suppression effect persists. If you're used to caffeine stimulation effect will be lower. You may have sleeping problems if you take them late during the day, they're supposed to be taken in the morning.

I would not recommend taking ECA long term. 2-3 months at a time should be enough to achieve significant weight loss. Just take them every day, and adequate dose, I've seen some people taking them inconsistently and that led to no results whatsoever and all the side effects, and Internet is full of reports of people who took too little ECA and it didn't do anything. Dose response seems to be binary, too low dosage doesn't work at all, very high dosage doesn't provide any more appetite suppression than normal dosage, but you get a lot more side effects.