[Galin]

Generally speaking (Appendix E), the runes were "devised and mostly used only for scratched or incised inscriptions" while the Feanorean letters were used for writing with brush or pen. With respect to the Feanorean letters, full modes had been reached, but older modes in which only the consonants were written with full letters, were still in use.

Of Dwarves and Men tells us that the Common Speech "had from its beginning been expressed in the Feanorian Script," and that writing with the Cirth was dependent on the already established usages of the Tengwar (the same text adds that the Dwarves, who preferred the Cirth, used a spelling that was intentionally "a transcription of the current spelling of the Common Speech into Runic terms”, yet this transcription included many words spelt phonetically).


I'd guess that the Hobbits were familiar with a full mode referred to as the "later or Westron convention, in its northern variety" (Pictures By JRRT) used by Ori the Dwarf in the Book of Mazarbul -- and (with slight differences), in the letter from King Elessar to Sam Gamgee (Sauron Defeated, Westron/English version).

Arguably (at least), and with respect to the latter example, this was chosen by a Gondorian as the recipients were Hobbits.