we have both; a polar A5 and a polar 720 series. the A5 lets you know where your horse's HRT is at any point during the ride but thats it. The 720 stores the data for computer download. We get a graphical download that shows heart rate and altitude over the length of the ride [we could add more parameters]. If you train on specific hills it really lets you see changes over time [for the good or bad]. side note the 520 has the same download features but lacks the altimeter and a few other features of the 720 series.
Conversely the 720 series uses a coded transmitter [T52H] which has a battery life that is half that of the un coded A5 transmitter [T51H] 2000+ hrs vs 5000, but it only costs $15 dollars to send it off and have the battery replaced on either sender by a service center.
If I was going to do it over again I would have only bought two of the 720 series model [we have two horses and one of us gets stuck with the A5]
