FWIW, it is also possible to get standalone induction receivers that you can plug headphones into, which can be useful for "is this working" checks (for example https://www.ampetronic.com/products/ilr3-audio-induction-loo...). However you really need someone with hearing aids to tell if it's useful or not.

I visit the theatre a lot: ~50 West End visits in 2025, plus several regional venues. It's amazing how many times I've had to abandon the hearing assistance system because it doesn't work well... too quiet, distorted, delayed, poor balance between voices and instruments. Sometimes it just isn't functional at all, and nobody's noticed.

While I'm on the subject: saying "it's a loud show, you'll be able to hear fine" is a bit like telling someone who's short-sighted but has no glasses that "it's a bright show, you'll be able to see". It's not just about volume, but clarity and understanding.