My understanding of the main mapping benefit of a 520 Plus vs a 520 or Wahoo Bolt is that is has on-board navigation that will continuously re-route in the event of a detour. In contrast, the Bolt will give TBT if the route was created properly (I use Ride with GPS), but if I go off-course the device is pretty dumb - it'll start chirping at me when I get close/cross my route again, but you're still on the hook for having a rough idea of how to get back to the pre-planned route (unless you want to stop and take out your phone).

Another 520 Plus feature that looks like it could be nice is their popularity routing (I forget what the TM'ed name is) which seems to be similar to using Strava Heatmaps for routing. Basically, you have the option of letting the device guide you based upon the routes that are more popular with cyclists (which are likely chosen vs shortest route because of more favorable traffic/better shoulders/fewer stops, etc). Could be a nice feature if you routinely find yourself in unfamiliar areas.

As mentioned, I have a Bolt and I'm very happy with it, but if I had to do it again, and at the same pricepoint, I'd take a good look at the extra features of the Garmin.