I bought this heart rate because the model ships by default with my 405CX (cardio "plasticized") gave some false readings, especially late in the race. Well, it says cardio "premium" is not better than the previous one ... Besides, just check the feet racing forums to realize that Garmin has never succeeded in producing a cardio reliable frequency.
The only interest of this cardio is its transmitter part / receiver that can come to connect to a Polar WearLink + (which also sells the only belt, without the transmitter / receiver associated Polar). We then have a solution that works very well, with correct measurements and cardiac compatible with Garmin watches / ANT +.