I should point out that we stayed in the apartment owned by this guesthouse, and not the guesthouse itself which is outside of central Budapest.
It's a very nice, spacious 1-bed apartment in a convenient area (situated near to Andrassy Ut and not far from the main stations) and with a porter on duty 24 hours and local supermarkets and takeaways. You can walk to the centre in 25-30 minutes or take the Metro which is about a 5-10 minute walk away.
The apartment was spotlessly clean when we arrived and the beds were comfortable. If you're the adventurous type who doesn't need to rely on a hotel reception desk for absolutely everything, then staying in an apartment is a great way to feel like a resident of the city, and the price we paid was very reasonable.
I recommend this place - well placed for the centre of Budapest, near good travel links, near the park and the Szecheniy baths (probably spelt wrong but definitely also worth a visit). Has a small kitchen, I guess my only complaint might be what they have stocked in the kitchen - I had serious difficulty getting into some cans with the opener provided. But if you want restaurants you'll find good food at good prices anyway.
And Budapest is worth a visit too.