they have to tune the DSP settings to get the amplification et al. profiles to match the patient's individual hearing loss pattern. that takes custom interface/

they have to tune the DSP settings to get the amplification et al. profiles to match the patient's individual hearing loss pattern. that takes custom interface/programmer hardware the manufacturers generally only (afaik) give to licensed audiologists as it takes specialized education to do this work properly. the ear dome/mold bits themselves are a minor component of the overall fitting process. (src: been wearing hearing aids for about thirty years)