Tracking revenue only would not reveal problems in the long-term benefit of the product - it would be more like a proxy for marketing actions, not for the core product benefit.
Still my favorite heart-rate enabled wearable out there!
New firmware and Android release coming soon that likely will help with your issue
The reason to track any metric is to know if you should continue, stop, or go all-in. If you are flatlining - or going down - that's a HUGE sign to quit. If you have steady growth, easy as she goes. Explosive growth, you might want to double down.
This is for pre-revenue companies. The expectation is that se will turn into revenue in many tech business models. Certainly for the type where you have to capture a dominant fraction of users to get the hockey stick curve.