Imho, just get a very cheep wired computer to put on the bike, and leave all the fitness tracking stuff to apps on the phone. I just recently bought a cateye Syria with cadence of fleebay. There were quite a few dealer that have them, all under $30 and most are new in the box. I run apps on my phone that keeps track of everything else. I'm planing on getting a heat rate sensor that will also talk with the phone apps.

I recommend a wired unit because you can put it on and forget it. My last battery lasted over 3 years, and the change out was about 15 seconds. In short, once you put it on, you just use it, don't have to screw with recharging or replacing battery's for a very long time

You can get a Bluetooth sensor to transmit cadence and speed to a phone app, but why bother? For $20 you have a very readable cadence monitor in real time, you don't have to remember to turn it on- it turns it self on when you start riding.

I'm not an expert on the apps. I have been using "mapmyride". What attracted to this product is the fact that there are thousands of maps others have made around my area to view. All of it is free. I have mine set so about every mile it gives me a "status report". You don't need a on bike computer to update the phone app. The gps inside the phone will do all you need for you.