If you're a B&S fan, you already own Dear Catastrophe Waitress, and you're buying this for two songs. If you are not, start with If You're Feeling Sinister.
That said, I like "Step Into My Office, Baby," and all of DCW. It's a different sound, but not unrecognizably different, and I had worried that the band would stagnate with Isobel's departure. Instead Stuart seems back in the swing of things, writing as well as ever, and the band sounds great. Some may say overproduced -- but I think one shouldn't complain about excellent orchestration and intonation.
But, you are likely wondering about the new tracks. "Love on the March" took a couple of listens, but I like it a lot. It's a lighthearted, cheerful song, which Sarah's singing adds much to. "Desperation Made a Fool of Me" is an excellent Stuart opus, in the classic mold although with new-style B&S touches. (The other reviewer's comparison to "Marx & Engels" is not bad.)
Ultimately, you have to decide whether to pay for just 2 new songs, but I think they are worth the price. (Then, I own every B&S album to date except Storytelling.)