Florence isn't a pretender, she can really sing. But if you disagree with that statement, if you didn’t like her previous works, then her MTV Unplugged session probably won't change your mind. She relies heavily on the impassioned wail that she's so very good at; her delivery's fervent, but it's Flo through and through, for good or ill. It's less stripped back than I'd have liked, it still sounds mostly like a full band - although I'd mourn the loss of the strings if they were absent, so I guess I'm as hard to please as the next person.
Her cover of the Cash/Carter song 'Jackson' with Josh Homme (of QotSA) was perhaps a bad idea. June did it a million times better.