Harry Turtledove has done a good job translating this snippet of Theophanes. The translation is crisp and most of the transliterations are well done. Occasionally some modern colloquialism sneaks in, but it is usually minor. Turtledove does an excellent job in rendering Greek wordplay and puns into English, and the fact that he cites it in the footnotes just goes to improve this edition.
Nonetheless, this edition isn't perfect. The issue of length may lie with the publisher, as Penn Press has similarly sized editions of the Strategikon and Gunther of Paris' history. Starting at Phokas doesn't provide the reader enough background, and while the text from Phokas on may be the only historically valuable part, would it have been so hard to add the reign of Maurikios? Additionally, the notes occasionally aren't all that useful or critical. While they often describe transliterated Greek terms, they are not sufficient to make this the standard edition of Theophanes. It's value lies in its availability and afford-ability, something that the Mango text cannot claim.