However, I happened to see a page from the Old Irish Book of Leinster that got me thinking about this again. I don't have much time (it's my lunch break) but I thought I could write a quick note about it.
The thing that caught my eye was the use of Tironian notes for their phonetic values. An example is the name "Conchobar", written (among other ways) as follows:
The first glyph in this name looks like a backwards C, but it is none other than the Tironian note for con:
Except, instead of representing the Latin morpheme con, it represents only the phonetic value. The same note is used in the name Conall. The RC does not look like a text that is written fully in Tironian notation, but it would be interesting to try to transcribe a sample of the Rohonc codex as though it were a subset of Tironian notation and see what it sounds like.
If you've ever wondered what a text written completely in Tironian notation looks like, here is a piece from the psalms, given at the end of a 9th century work titled Comentarii notarum tironianarum: