Hi, I’ve been usong this app on my Apple watch. The nice thing is that you can chose 4 or 5 zones and that you can customize these zones manually (on the Apple watch you can atm only work with 5 zones).I look daily in my Welltory app for the zones and adjust them in Zones if necessay. The sounds (bleeps, these could be a bit louder please) and vibrations when going from one zone in another are very handy. If you do not want a heartrate strap this app also works fine on your Apple watch in your swim workouts (make sure your watch is tight on your wrist). Also results of workouts started from other apps such as the Apple workouts, seemlessly appear in Zones. I use zones for walking, cycling and roeing too. It is just great. Unlike Apple Watch it shows the average intensity and intensity range of your heartbeats too. Zones cannot cast the heartbeat to the PM5 monitor of Concept2, nor can Apple workout, but if you use a Polar H10 you can broadcast your heartbeat over bluetooth to your Apple watch (and thus to Zones) and to your Rowerg and PM5 monitor of your Concept2. Of course using the strap will result in a even more concise heartbeat monitoring.