I previously used a Polar S725, have had an Edge 705 for a couple of years, so older versions of each, but the Garmin is far better in every way.
Even taking the mapping out of the equation the number of fields is better on the Garmin, the numbers are easier to read, it handles interval sessions better (the inbuilt interval thing in the Polar S-series could only manage intervals of one length, no pyramids or owt, may be different on CS-series). It doesn’t need sensors on every bike, it’s easier to upload to WKO, Strava etc (again, dunno what the interface is on the CS ones but the Infra-red on the S725 was crap).