SWWLTBO has a student who suffers arthritis and has this bit of kit. She has had problems with "training it" to understand her and required a great deal of help to set it up. It still gets confused by her accent from time to time. Such things are fine for the handicapped (for whom it is intended) but it does seem to take some time to get it right for you. Not just plug in and go I'm afraid.
That said Stephen Hawking manages to use it.