Moderately deaf Brit here. The NHS used this technique on me a year ago when I got my hearing aid. Whether it is imprecise or not I don't know, but it generated a graph plot showing, for each ear, a plot of my hearing response against a range of different frequencies, which was annotated with the position of specific phonemes - so I could see which vowels, etc were hardest to hear. This seemed to match my experience, although I didn't test it rigorously.

If you are reluctant about getting a hearing aid, I would totally totally recommend it. It turned my social and professional life around - I was beginning to avoid conversation with certain softly-spoken people and couldn't follow arguments in conference rooms that had any sort of noisy aircon. As a Brit, I have access to free NHS hearing aids and consumables (batteries and the tiny tubes that go into the ear), which helps. I had been planning to buy a smaller in-ear device, but in fact the external device is acceptable in terms of size and appearance (silvery grey).

The device I use has an external control button (a tiny stud) which controls volume but which could alternatively be programmed to trigger different modes (e.g. noisy room vs quiet room). The fact that I almost never have to change the settings also suggests that the initial test (which is programmed into the hearing aid) was somewhat accurate.