In general they will produce better rice than most people can make using a traditional pot. I certainly get excellent results with mine, which is a Zojirushi model that uses induction heating (IH) technology, and cooks rice under a high level of pressure.

Most rice cookers will do a good job, but the best ones use induction to cook the rice (and keep it warm), and are "pressure type" models- ones that cook rice under pressure. These will produce better rice, and keep it nicely warmed and ready to eat generally for about 24 hours (or even longer, but I prefer to make fresh rice each day)