So when the vowel does not cause an on glide, is the consonant essentially the same and the broad consonant (except in obvious cases like s and d and t)? Basically, is the “m” in “mé” the same as the “m” in mo?
No, the broad and slender consonants are quite different. For instance the difference between the b in beo and bó is the main difference between the two words.
The off-glide is simply a natural by product of the tongue moving from its position while making the slender b at the start of beo to its next position while making the ó.
By the way, the written “e” in beo is present because the Bard’s who encoded the modern Irish spelling conventions at the end of the 12th century analysed the tongue to be in the e position while slender b was being uttered. It’s the same for all of the (silent) broad/slender marking vowels.
