With respect to directional properties, the few studies available presenting an intermediate level of evidence allow us to classify as 'experimental' technologies both single-microphone solutions and approaches based on a microphone array. These solutions seem promising, but additional controlled trials will be required to confirm their efficacy.
Dual-microphone approaches can be considered 'accepted' technologies but only in optimal listening conditions, when the speaker and the noise are diametrically opposite each other in rooms with low reverberation. The application of this technology in other conditions reduces (sometimes significantly) their effectiveness. Finally, eligibility requirements for devices with the directionality option must take into account the candidates physical and cognitive abilities to use the directional properties effectively.