Its not that it is "no good", it is just that chlorine is enough better that there isn't really any point in thinking about bromine for a pool. Bromine is more sensitive to sunlight than chlorine is when using CYA, so you end up spending more money, and many people object to the "chemical" smell. Bromine is more stable at the high temperatures in a spa, so bromine is better in a spa, but in a pool chlorine is the clear winner.