Both units will know exactly your current location and get you to your destination.
How you get there & how both units support you along the way is a different matter. In this case, my preference is the Edge because of compatibility with large number of mapping sites, support for loading custom points of interest, and huge supporting community of Garmin users.
I was going to get the Garmin Edge Touring Plus but then started reading about how inaccurate it supposedly is, is this really the case?
What measurement is this accuracy claim in reference to?
For knowing your current location, no doubt that both units have the same accuracy based on the GPS chip, to within 3–5 meters of current location.
For calculating the route between two points, each unit has its own calculation method. I would not trust either completely without verifying the route in advance, unless it is necessary or required such as in the case of road closure, need for urgent bicycle repair, etc.
Regardless, while the calculation may be different or the units may have a different way to connect two points, they both will get you there. Just be sure to set your preferences correctly in the unit, for example, to avoid highways.
Then I started reading about the Magellan Cyclo 315 which on the surface seemed to have more detail about certain things like nearby bicycle shops, restaurants, and cyclo lanes that Garmin doesn't mention which I find odd since they both use the same OpenStreetMap.
The Cyclo did find more service points near me compared with the Edge. It also has a convenient top category for bicycle shops. However, when I select that category in Boston, it does not find any bicycle shops!
I would not rely on finding service points in either unit. Smart phones, if you have one, are far superior in finding services.
Note that the Cyclo does not support loading points of interest onto the unit from an external source. You can only define them manually in the unit.
This is where the Edge shines given all the external support you get from Garmin BaseCamp mapping software, Garmin Connect web site, and direct connectivity from most mapping web sites out there, such as Ride with GPS.