I was lucky enough to play this instrument a couple of times when I was a teenager. Apart from being very heavy to play with all manuals coupled (there is an 'assistance' stop which is meant to help) I think it is a fantastic instrument.
I can see how the mixtures seem strident to some, but I actually quite like the clarity and brightness.
I also particularly like the bombards on the pedal which sounds unlike any other I've heard. It's powerful but not 'muddy'.
The 'dermogloste' stop intrigued me too. I think it is unique to Beauvais. Some kind of free Reed I think. Wish I could remember what it sounded like.
Jennifer Bate and Jane Parker-Smith's recordings there are still amongst my favourites. Although Olivier Latrine's Messiaen is perhaps pipping Jennifer to the post at the moment.