Good video overall, though I would comment on his pronunciation of the word buí. He states that to pronounce buí with more of a 'w' glide would be incorrect, though I would somewhat disagree. I think that the main reason for him saying this is to help discourage learners from placing 'w' glides in between all broad and slender vowel-consonant groupings (i.e. encouraging caol rather than cwaol), but words such as buí and baol tend to have somewhat of a labial(-velar) glide in native speech, as the position of the lips when making the 'b' sound already set up the glide for an active labial position. The most important part of getting the glides right, I would say, is that your destinguishing broad and slender consonants. Even when not in the position for an obvious glide, for example, the broad phonemes will still have a velar componant, i.e. the b in bó (/bˠ/), though because there is no shift between a broad consonant and a slender vowel, this labiovelar glide won't be present (i.e. not /bʷoː/). I would agree assessment that the more Anglacised pronunciation BWEE is incorrect, though, as there would be no apparent velar or broad quality to the /b/ phoneme, i.e. just a neutral consonant followed by the approxomant /w/, whereas natively it would be pronounced more along the lines of /bˠwiː/ or /bʷiː/ (with the /w/ sound less enunciated than that of English, of course). Obviously this isn't always consistent, not even among individual speakers. If you search many phonetic works such as those of Heinrich Wagner, you will find plenty of 'w' between broad labials and slender vowel sounds, along with those without, suggesting a purely velar glide. Irish glides have very very diverse phonetics, and this video only goes of half of them (the broad glides), but like I said, a very good video of native pronunciation outside of what many learners will hear. He makes a great point that glides will often come naturally without much thought between two phonemes if you already have a good handle over broad and slender consonant pronunciation, but listening to native speakers is also the best way to practice.

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar

Interesting way of teaching it. I think it hammers home the point that teaching the language needs to start with mastering broad/slender phonetics - once those are sorted, a lot of other things fall into place.

E.g. his (broad)G -> ae -> (slender)L example in Gaeilge, which learners frequently assume is a phantom 'w' sound. It makes more sense as a transition between specific broad/slender consonant sounds, but if the learner doesn't have that foundation (e.g. is unfamiliar with broad and slender L sounds) then they'll never make that connection, hence "Gwaylga" is their nearest approximation using English sounds

Mandarin education takes the assumption that learners first need to learn a new and unfamiliar set of phonetics (e.g. 'zh' sound), so in addition to the basic "hello my name is" starter vocab, there's extensive phonetic drilling to ensure basic sound combinations are mastered first. I wonder if something similar would work for adult Irish learning