they work, but once they eat the algae they will starve to death..depending on the slug it may excrete a poison into the tank,so do your research before you add them to the tank.
150ppm is OK, but I was able to get away with raising 200ppm a day.
Once you get to 1700ppm, you need to leave it at this level for at least 3 wks..if you need to do a water change for any reason, dose again until you get back to 1700ppm..then monitor until bryopsis is gone.
to use a crewd wrestling analogy, get the bryospis in a head lock and don't let go, if you need to reposition yourself (that is, a water change), resume headlock until you choke the living <beeep> out of the bryopsis until it gives up.
Consistency and determination is required when fighting this algae.