I would be reluctant to use a device that keeps live bait on a hook
even if someone gave me the device. The main reason: I'd suspect the
fish would be turned off by the retaining device. They might not
bother to bite when they see the device, and if they do bite, they
might quickly get spooked by the unnatural feel and bad taste of the
device.

In an old tackle box originally belonging to my grandparents, there's a
device intended to keep minnows on a hook without being stolen. It's a
mesh container. Haven't used it, figuring the mesh would reduce the
bait's ability to twitch along with the above-mentioned visual and
tactile turnoffs. Apparently that idea was discontinued 50+ years ago.

Worst of all, I believe the bigger the fish and the more special the
species, the more likely the fish will avoid the retaining device. A 4
or 5 inch Bluegill might not mind, but a 7 inch Bluegill that would
bite a regular hooked worm might avoid a retained one, and other
species such as Catfish or Carp might avoid the worm entirely. One
reason I use worms is the chance of something huge or unusual biting.

Stolen bait is a fact of life. One way I cut down on lost worms is to
use pieces instead of an entire worm.

One bait that should be protected is chicken livers because they're
incredibly easy to steal. Have hear a good protector of chicken livers
is cut pieces of stocking/hose, then enough for the scent of the livers
to seep through.