I use both a Garmin 530 and a phone app called Ride with GPS which was free. The Garmin adds a lot of detailed info to my rides like heart rate, respiration rate, vertical distance climbed, it’ll also take power meter inputs but I haven’t bothered getting power meter pedals yet. It sends all that data to my phone’s Garmin app so I can go back and look it over later.
The free Ride w/GPS phone app has great mapping so when I go way out of town I can quickly see “where does that road go?” or find my way back to my car! It’ll also tell you average speed and max speed. It also has a lot of the trails in the woods where I ride my mountain bike which is nice.