To add, a few selected quotes from his direct disciples:
“Yogi, practise the samatha kammatthana: the metta kammatthana and Buddhanussati kammatthana. To develop the full strength of samadhi, don’t you have to get the help of samatha kammatthana? (Ashin Kundalabhivamsa, Correct Way of Progressing to Higher Magga and Phala: 45)”
“Only when samādhi develops, vipassanā ñāṇa develops. (Ashin Kundalabhivamsa, Nine Essential Factors Which Strenghten the Indriya of a Vipassana Yogi: 30)”
“Since metta is easier for most people to develop and it benefits everyone, the practice of loving-kindness really ought to become widespread. (Sayadaw U Pandita, Get very, very close)”
“I had practised without any sleep continuously for about fifteen days. (Sayadaw U Jatila, Dhamma Discourses: 21)”