The sure test looks nice and may be great for some things but I believe it does have issues.
One day we did a panel upgrade for a home inspectors house. While doing the job he said something like "How come most electricians never ground the outlet next to the panel right? Seems like every home I inspect the GFI by the panel is done wrong".
Around here everything is pipe and steel boxes so I just figured he was talking about installing a bonding pigtaiol from the box to the GFI. Not wanting to have an issue with the HO we ran an EG from the GFI under the panel to inside the panel.
Finishing up the home inspecters job he pluged the Sure Test in and said we did not ground the GFI right (in a metal box under the panel with EG to the panel). Looking at the tester it said something like "faulse ground". Tried it on other locations and any box near the panel would say "faulse ground". Figured out the tester could not see enough differance between the EG and the Nut on devices close to the service so it thought the EG and Nut were tied together on the circuit. Every home inspection he misdignosed the panel GFI's as being a faulse ground.
