I was going to suggest "Ride Report" android app, because it automatically detects when you're riding and syncs it to Strava. You don't have to start the app, touch a button on the app or anything else, it just runs hidden and does it.

But that doesn't provide cadence distance and speed. I think if you want all that plus auto syncing to strava, you won't find it in a cheap bike computer. Plus, it's going to need network connectivity of some sort to talk to Strava, and if you have to take it off and plug it into a USB cable every ride, that's not very automatic. Maybe there's a Garmin model, but not cheap. My suggestion is to use a cheap wired computer for candence and speed, and use the phone for Strava.