Distinguished both in his lifetime and after, his compositions were studied and used as exemplars in medieval metrical tracts.
The Annals of the Four Masters state that: M891.14 Flann mac Lonáin, Uirghil Shil Scota primh-fhileGaoidheal uile, file as deach baí i n-Erinn ina aimsir, do mharbhadhla macaibh Cuirbhuidhe, do Uibh Fothaith iat-sen, h-in-duinetaidhe h-ic Loch Dá Caochi n-Deisibh Mumhán.
M891.14 Flann, son of Lonan, the Virgil of the race of Scota, chief poet of all the Gaeidhil, the best poet that was in Ireland in his time, was secretly murdered by the sons of Corrbuidhe (who were of the Ui Fothaith), at Loch Dachaech, in Deisi Mumhan.
The Annals of Ulster state that: while the Annals of Innisfallen notes; while the Chronicon Scotorum more fulsomely records that; In his posthumously-published work, The Irish Tradition (1946), Robin Flower wrote at some length of him and the legends surrounding his life.
Flann is mentioned in the oldest surviving personal letter from Ireland, which dates from the mid 12th century and was addressed to Áed Ua Crimthainn, compiler of the Book of Leinster, by Find, Bishop of Kildare, who wrote: "Let the poem book of Mac Lonáin be brought to me so that we may study the meanings of the poems that are in it, et vale in Christo.