Michael Chare wrote:

I would like to persuade an elderly female relative to try a hearing aid.

I wouldn't buy anything for a trial. There are commercial hearing centres
which will carry out a basic hearing test and program sample hearing aids
(possibly more than one model) for your relative to try. There's no
obligation to buy, so if she likes the result the next step is to go to her
GP and arrange an NHS test. If needed, they will supply very discrete,
modern, programmable hearing aids (and free batteries).

Some commercial suppliers occasionally run public demonstrations, usually in
hotels. They advertise in local papers, so it might also be worth keeping
an eye out for that.