I have used Sygic several times- I have a work cell phone, and a 3$ per month throwaway for travel.
3$ phone has no data, so II need offline GPS.
The hard part was pre-downloading the maps for areas that I needed, but once that was done, it worked very well.
USed no data at all....
Did Minneapolis, Denver, Washington DC that way. All maps were accurate- just no traffic reports (duh)