It works in a limited number of cases, but it has the advantage of producing the most natural sounding speech in a restricted domain. The approach is not compute intensive.
Quality varies widely from barely intelligible to human-intelligible.
The principal drawback with diphone synthesis is that the underlying model is fairly restrictive. Though systems like GalaTea achieve a fair amount of intonation, the intonational structure generated still leaves much to be desired. The model also allows only minimal variations in voice, e.g., pitch and speech rate. Changing voice parameters produces a significant deterioration in output. It is also the most flexible approach to speech synthesis.