If you have your hearing tested by the NHS, it is free, as will be your hearing aids and batteries. There are though, as you might expect, many advantages to having Hearing Aids prescribed through a private 'Dispensing' company or individual. These include
Service: private Dispensers have more time for you. Private Hearing Tests are, however, free, just as NHS tests are.
While investigating the history of your 'Hearing', which can assist in providing a tailor-made solution for you, the NHS will not have anywhere near as much time to dedicate to you as a private audiologist. A typical NHS consultation last for only 45 minutes, which is not a long time to solve a problem (if there is one) concerning one of your most vital senses. 'Private' dispensers/audiologists work under a strict code of practice, which means that you will get the best advice in relation to any hearing test results: if you will not benefit from a Hearing Aid, a private dispenser will tell you this.
The choice of Hearing Instrument is very wide indeed from a private dispenser: the NHS provides only a very limited choice, and within that choice it is very unlikely that the NHS can provide one of the very tiny, discreet 'in-the-ear' hearing aid systems.
If you are in any way unhappy with a hearing aid dispenser who visits you, you can show him/her the door, and book an appointment with another company.