My solution to a simple, intuitive gps-based navigation device is a Suunto Ambit watch (specifically an Ambit2, which is the previous model to the current Ambit3 and hence can be picked up for under £200 if you shop around). I don't use a Mac, but know for a fact that they work perfectly with a Mac as I have at least one friend who uses that combination. Data transfer is via a cable and monitoring program constantly running on the computer, so transferring routes to the watch is just 'plug cable in' and the same for extracting data after a ride. Pre-existing gpx files can be uploaded to Movescount directly into routes and these will then sync to the watch.
It links to Suunto's Movescount web application, which includes a very easy to use, intuitive route creation facility. (It can be made complex, but the obvious way to use it is intuitive and effective.) All I do is create a route then annotate it with points of interest which, in the case of audax rides, tend to be simply left, right, bear left, bear right, cross, summit, etc. i.e. short statements which I put in at any junction or feature of note for navigational purposes. It's pretty much a transcript from a route sheet. It requires looking at where I'm going to go before setting off and considering whether an instruction is needed / interesting / useful, but I see that as good thing since then I pretty much know where I'm going, as I would do from perusing a paper map in advance. 100m. before any of these instructions, the watch beeps (quite loudly) and displays the instruction in large letters for a few seconds. Between those nodes I have the watch displaying distance to the next instruction / node / waypoint, in large type. Very simple, very clear and very like a route sheet which is constantly highlighting the next instruction. If someone gave me a dedicated cycling Garmin device, I'd not use it. Oh, and the other benefit is that battery life is between 16h and 50h, with the gps active and recording, depending on accuracy settings.