Wahoo requires the entire setup of the device be done via an app on a smartphone or tablet, Android or iOS works, Garmin you can use out of the box without connecting or use of a phone or tablet. You can setup the recent Garmins to a WiFi connection and download navigable routes created on assorted web based apps, Connect (Garmin), RideWithGPS, Strava or Kamoots. The Garmin iQ app on the device can find created routes on Connect, RWGPS or the others, thus no phone needed, just WiFi. The Wahoo units need a phone/tablet with the app to download routes. In general, the web apps allow you to create a route online and download to the device. You can, in theory, create a route directly in a Garmin device and use that to navigate, never done that’s as it a frustrating
process on the small screen. I think the Hammeread K2/3 works like Garmin, a web based app to create a route then sent to the device via WiFi. Hammerhead only recently started using an app on a phone, not sure what it does, the K2 never had an app.