The bottom line is what functions are you using with your clients. What functions do your clients use independently of when they are with you?
New clients often do not need detailed functions, but just the basics. Heart rate monitors must be an effective tool for the client, and not what the trainer thinks is best. In other words we may like the multiple functions because we use them, our clients may not.
Polar is excellent, but my old model does not allow me to change my own battery locally, I must send it in. Other models are less expensive (Omron $35) and may fit client needs.