Mru and Anu-Khongso are two closely related languages. Both are sesquisyllabic and SVO. Mru-Khongso have clearly undergone phonological and phonotactic influence from Austroasiatic languages. Austroasiatic lexical influence is more limited, and not as extensive as in Lepcha or Kuki-Chin. Nevertheless, some words of Austroasiatic origin can be seen in Mru and Anu-Khongso, such as the word for 'grass' in Khongso.
Similarities are shared with Bodo-Garo and various other Central Sino-Tibetan branches, pointing to the position of Mru-Khongso as an independent branch with Central Sino-Tibetan. Kuki-Chin influence is relatively recent.
Mru-Khongso is definitely not Lolo-Burmese, contrary to Löffler (1966). Its autonym is reminiscent of certain Austroasiatic autonyms such as "Bru." Austroasiatic words that look similar to "Mru" include Proto-Austroasiatic *mraʔ ‘person’ (Sidwell & Rau 2015), Proto-Khasic *brəəw 'person', Proto-Khmuic *-brɔʔ 'man, person', and Proto-Khmuic *kmraʔ 'person' (MKED database). Mru does not appear to have many Austroasiatic loanwords, but its phonology is highly Mon-Khmer-like with sesquisyllables, final liquids, and initial consonant clusters with liquids. A similar parallel is Kerinci Malay, which has a Mon-Khmer-like phonology with sesquisyllables and Mon-Khmer-like diphthongs, but no recognizable Austroasiatic loanwords. However, there has not yet been any solid argument for Mru having an Austroasiatic substratum. Peterson (2009) notes similarities between Mruic and Bodo-Garo. My personal view is that is in DeLancey's (2015) Central Tibeto-Burman group, but does not subgroup with Sal or Kuki-Chin-Naga languages. I have found that Mruic has some similarities to Sal languages in general, not just Bodo-Garo, which would mean that Proto-Mruic would have been in contact with Sal languages in the Chindwin River valley.
Recent data on Anu-Khongso have improved the situation, making it possible to reconstruct Proto-Mru-Khongso.
Sound changes
Key
C. = sesquisyllable ("tightly attached")
C- = disyllable ("loosely attached")
Sources
Luce, George. 1985. Phases of Pre-Pagan Burma: languages and history (volume 2). Oxford University Press.
Language and Social Development Organization (LSDO). 2009. Initial Sociolinguistic Survey of the Anu, Khongso, and Asang Varieties in Southern Chin State, Myanmar. Unpublished manuscript.
List of reconstructions