ðɪ ɪfˈɪʃənsi ʌvðə sˈɪstəm hɐz haʊˈɛvɚ nˌɑːt bˌɪn sˈʌbdʒɛktᵻd tə səfˈɪʃənt kəmpˈæɹətˌɪv ˌɛndʒɪnˈɪɹɪŋ ɹᵻsˈɜːtʃ.
The efficiency of the system has however not been subjected to sufficient comparative engineering research.