Power meters were invented and used to be applied to biking systems since back in 1989. Essentially a power meter gauges how much power output is being created as a direct result of the exertion that the rider is applying to the bike. There are many kinds of meters nowadays, each with their own benefits and pitfalls. The chain power meter, particularly, is a mountable meter that is applied to the chain stay of the bicycle and then measures the amount of power output by interpreting the vibrational data of the chain into tension data. That data computed together with the speed of the chain, calculates a figure for power output.
At its most basic, the meter is just an add on, while some models include a vast system that measures much more than power output, such as heart rate and so on. The obvious advantage is the mountable application, that can be applied and removed rather easily, which also speaks of its novice level installation. A pitfall, however, as has been mentioned by users, is that at times the sensor is too close to the chain stay causing spatial problems as well as potential damage. The next obvious question is one of accuracy. Is it more or less accurate than any other power meter out there? The answer is based on percentage rather than exact figuration. It is not so much that it is accurate, but that its chances of inaccuracy are between one and five percent.
That being said the chain power meter may vary in advantage simply because of price alone. On the other hand, weight is a considerable factor as well. Because the chain meter can be mounted, rather than replacing a bike component, it may weigh less than other meters whose integrated meters weigh more due to additional mass within specific components.