[wswartzwel]

I use one on my road bike to show my cadence for training purposes... and a speedometer is nice if riding with a group so you can maintain a constant speed when it is your turn to ride in front.

For keeping records of how much I ride in a year and to monitor progress a simple phone app like strava works just fine. Hope you and your wife enjoy cycling as much as my wife and I have. First hobby we have found that we can enjoy together.