Of course it all depends on your goals.

For cadence only, I'd probably hunt for a cheap handlebar mount cycle computer that has speed + cadence. I don't know if the cheap ones also include HR. But, for the most part, I prefer the cheap handlebar mount computers for real-time speed.

I like using Strava and/or Ride With GPS for my ride tracking. RWGPS tends to give better real-time data. Strava gives good off-line data analysis. Plus, Strava's "segments" are fun.

I run Strava off-line, so I've memorized where the segments are that I want to use as a challenge.

One can also create segments, either personal or shared that you can use as part of your workout routine.

I've had troubles earlier getting external sensors to synch with RWGPS and Strava on my phone. I suppose it is time to try that again.