Probably some English native should write something...
Just one thing where I can easily notice that the pronunciation has both US and UK elements, like the word "rather": in the standard (
RP) UK dialect (and I'd say probably across most of the England; probably not Scotland) the "r" is pronounced these days only on the beginning of a word (where it tends to be more with rounded lips) and between two vowels. But before a consonant and in the end of a word (unless in connected phrases as "far away") the "r" is pretty much dead in the UK dialects (probably save some Scottish ones(?) ) but it survived in all positions in the general American pronunciation (
GA; and afaik in most of the American accents - maybe not in Boston?).
Also that pretty much means that if French speakers don't really like learning new r's (but you do it well!) they can just go with the UK accents and still sound genuine
So, as a foreign language speaker, once you pronounce "r" in all positions, you pretty much out yourself as a US accent user (or GA) but then for the "a" before "th" (rather, bath, path) or "a" before "ss" (pass, but also sometimes before "s" as in "past, ask, answer") you can't use the Brittish vowel which is pretty much alike the Latin/French "a". The American dialects use in all these words the vowel that you can here e.g. in "bank" or "lamb, damn..." (sometimes they tense it more so it seems also longer).
(Here are the transcriptions + also audio)
So this is for example how I can easily recognize whether a European foreign speaker (who is usually taught predominantly the Brittish use in school/most courses but hears just American stuff in the media & on the internet) consciously tries to differentiate between these pronunciations or not: you either don't use the "r" and use the same vowel (similar one) which is French/Latin "a" (almost the same), or you use the "r" and but use the different vowel as in "bank, ran, sank, ....".
I guess that the Boston(?) US dialect would also permit to use the other vowel (bank) and not pronounce the "r" though
But sorry for this awful wall of text + I'm not even a native!
I'll be happy if some native speakers (or those who have grew up in US/UK since their early childhood) join and give us more feedback

I'll certainly post something also... I just have to think what .P