We took this particular tour in late August 2011. I recommend it highly. Our guide was extremely knowledgeable and pleasant, with amazing English. Budapest is actually quite a large city, in terms of distance, and so touring by bike was ideal for viewing the city. We visited lots of the main sights, won't list them all as I'm bound to forget some!
Most of the routes we followed were really flat and we were never in heavy traffic, always on the pavement or on bike paths. We had a delicious lunch half way through, our guide told us they'd changed to this new restaurant in the summer of 2011. It was really tasty and a good break in the middle of the trip, without being too heavy to keep cycling!
I've seen a few comments on the climb at the end of the tour, I didn't find the climb bad at all - all the bikes have good gearing on them and it's not long, you just need to put it in a low gear and trundle up the hill. Well worth it for the views!
This is a small family run company (our guide and his sister own and operate it) and it was an extremely pleasant experience. I would highly recommend it to anyone who enjoys cycling as a way of seeing cities.
Also, Budapest in late August can be VERY hot - if you have a hat that will stay on while cycling, then take it! And lather up in sunscreen. The day we went it was over 30 degrees and it was much more pleasant to be cycling than walking - our guide kept us in the shade most of the time, was great.