For me it is very accurate (iP4, o2) when I’m in central London, when I’m at home (Herts) it occasionally thinks I’m about a mile down the road.
I have a JB’d iP4 with PlanetBeings ‘Signal’ app installed, when I noticed the location was off I loaded signal and it showed I was connected to a GSM tower about 3 miles down the road, not the tower slightly closer in the opposite direction.
I can only assume its calculated my location from this tower, I also had poor signal at the time.
EDIT>
I just loaded Signal to check, It showed me connected to the furthest tower and my location was about a mile out, then it connected to the tower closer to my house and my location changed to exactly where I am.
So, its due to the tower its connected to i guess. I only purchased Signal to support the Dev, never thought I’d use it!
EDIT 2>
Anyone using Signal should update in Cydia, and always remember to terminate the process when done
