I stayed here with my family while attending the Musikmesse. The location is fantastic--you're less a kilometer from the Hauptbahnhof (if you take the right streets), and it's easy to walk to the Musikmesse, the Alte Oper and central eating/shopping district, as well as the river. Of course, this also means you're not far from the red light district, but the neighborhood where Dirazi is located is quiet; an upscale bedroom community for the financial district folks, nestled in between bank skyscrapers.
The rooms are spacious and very comfortable, with clean, modern furniture, good internet access, TV, and small, mostly unstocked kitchen facilities. The beds were great: some of the best sleeping on our worldwide trip happened in this guest house. The breakfasts, served in the room, were quite good---the croissants were the best I've ever had outside France. However, the breakfast costs extra. For our family of 5, that meant an extra 30 euros a day on top of an already expensive stay. For what they're charging, you'd think they would just toss in the croissants.
I think an earlier review used the phrase "Teutonic detachment" to describe the German owner, and this is not far off the mark. He is efficient and polite, but not exactly warm, welcoming, or engaging (his Italian wife is delightful). No worries, though--the house has plenty of charm, cool old staircases (not for the weak-kneed), and a primo location. If you don't mind spending a few extra bucks, it's a nice haven in the heart of Frankfurt.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC