I have said it before on this forum and will say it again, a voltstick is only useful for stirring your brew, Why anyone would feel confidence with one is beyond me.
Also while on the subject of safe isolation, less than 2 weeks ago we tested a couple of offices/ cabins for a regular customer which threw up some remedial work one of the jobs was to replace 25 socket fronts that due to being painted had started causing issues when trying to switch the sockets off on the faceplate.
So in we go saturday morning ( only time we could shut it down ) anyway in the board there are 4 mcb's 3 x 20 for sockets 1 x 6a for lights I switched off all 3 socket mcbs but my socket tester still indicated power so even turned off the lighting with no luck.
The long and short of it was the mcb for my required cicruit had gone faulty so still allowed voltage through. I bet a lot of guys would have not tested the socket if they had all circuits isolated, that's why it's crucial to test, test, test.