Product review (2 stars): Assume until proven otherwise...
The cartridge I received this time never worked - but by the time we diagnosed it as the problem (v. other elements in the system, because I just didn't believe this could be defective, duh...) the return window had closed.  Second (yes, sigh...) technician said it's not unheard of for the cartridges not to work, so learn from my experience - install promptly, assume until proven otherwise that it is the problem if your system is working before you installed the new one and return for replacement if you get a dud.  I have bought other, identical ones on Amazon that worked fine.