My navigation needs are pretty basic in that all I want a computer to do is guide me along a pre-planned route. (From RidewithGPS). For this, I find the Edge 520 more than adequate.
Yes, the included map is useless but putting more detailed mapping on is not difficult. If you are prepared to do without street names then you can get quite a large area on there. (I have most of Northern England on there which takes up all of 4Mb, and you can probably just about get the whole of the UK on there if you want).
I've certainly had no problems with it navigating me along a route that I probably would have thought twice about due to multiple badly signed junctions.
If I did go off course for some reason, or need to change my route, I have maps on my phone that don't need a data connection to get me out of trouble.
My only minor complaint would be that the beeps that warn you of upcoming junctions are not loud enough. (Though they are louder with the plastic mounts than the out front mount).
I'm not knocking the Bolt, and I think that how it integrates with a phone is quite neat, and if I had a compatible phone already with a data plan, I might well have bought one. As I mentioned though, my phone is not compatible, (but otherwise works fine), and I wasn't prepared to buy a new phone just to be able to use a cycling computer.