Pretty slick.  It's genuinely hard to tell what the hell the TTS is saying at first.  Festival is a huge PITA to install but you'll get much better results there, or just record your own prompts.  (I know, no one likes the sound of their own voice.)

All I did was deposit a tiny amount of money and listened to it announce the unconfirmed transaction.  The only problem I found was after I had chosen to hear my receiving address: after the confirmation part, the canned prompt said "press," but then no "any key" as I would have expected, and it then looped, repeating the address.  I just hit 5 to get out of that and back to the main menu.

You might want to have it express capitalization during the quick confirmation phase.  I wasn't paying attention the first time around and missed that one of the letters was capitalized.  It also seems like it might be easier if it explicitly says "lower-case," to avoid confusion, and keep a constant rhythm.