I have a Zumo 590 (as well as a 660 on my other bike), and I use BaseCamp.
I wasn't too happy about being forced to go over to BaseCamp - this because MapSource, the predecessor of BaseCamp, does not support the 590 - but after having used BaseCamp for about a year now, I've pretty much figured out how it works. BaseCamp is not one of those applications that you can figure out by intuition, but once you do get it figured out (in my case by watching videos that other users had put on YouTube), it's pretty easy to use, and certainly more powerful than MapSource.
I'm happy with the Zumo 590. The thing was dreadfully expensive, but it is really easy to see in bright sunlight, does its calculations and screen re-draws very quickly, and the Bluetooth, tire pressure monitoring, and phone integration all works well.
Another forum member mentioned (above) problems with the route changing a bit when the route is exported from BaseCamp to the GPS device - this problem can be overcome by ensuring that you are using the same version of the map on both devices, and/or by selecting the option to 'export shaping points' when you export a route from the computer to the device.
All in all, I am satisfied with both BaseCamp and the 590.
If you are in the Toronto area, send me a PM, you can come and look at the setup on my ST1300 and I will give you a quick introduction to BaseCamp.
Michael