I can't understand the people who say they are useless. Have you never had a box with a dozen or two cables criss-crossing from one conduit to another, where you need to find which one to tap into or divert? Unless you use a non-contact indicator, you've got to cut a cable, test it, then joint it back together if it's the wrong one, which is daft. Or halfway along a trunking run with 57 cables in it, try to find all the reds that belong to one circuit?
These are common problems in telephone and data work where there might be 5,000 cables. With an oscillator and tone tracer you can sift through them and find the right one in a minute or two, but you've got to connect the oscillator to the circuit first. I sometimes do this with power circuits too but it's no good if the circuit has to stay live or might be live. The volt stick allows you to 'tone' a cable while it's still in use, because the mains is its own 50Hz 'tone' that the voltstick looks for.
Then, how about proving dead at a point where any or all of L, N and E might be damaged? If the N & E are severed but the L is still connected, an approved indicator will say it's dead while the voltstick correctly indicates that it's still live.
Horses for courses, so I carry both (and a donkey) in my toolbox at all times.