Like any other instrument, Alternating-Current non-contact voltage testers require experience to safety/effectively use. I feel they improve overall electrical safety, if not used "blindly." Clearly there are various grades and prices for the devices. The technology is used daily up to 765kV. Combination flashing-light/audible versions are desirable.
Not verifying on a known-live source immediately before and after proving a deenergized circuit can be suicide.
