The cal hypo pucks are made by Arch Chemical under both the HTH and Poollife brands. Get the Poollife Active Cleaning casules. They don't dissolve as fast as the HTH Duration ones do. They are designed to be placed in your skimmer, NOT in a feeder or floater and CERTAINLY NOT in a feeder or floater than has held trichlor. Cal Hypo generates a lot of heat and give off a lot of chlorine gas and to use them in a feeder or floater can lead to an explosion.
They will not last as long as trichlor and, in actual use they are gone in about 3 days so they are not a viable alternative for using during an extended vacation.
PPG also has a cal hypo pool chlorination system but it is more than just the tabs. It is a set of chemicals, the tabs, and a special feeder. It will help avoid overstabilization but you also have to look at cost effectiveness. The system is called Sustain.