If you look at some of the older threads there is 2 or 3 about the Fying pigeon in the last 1-2 weeks. At least two peopel bought it an wrote about it. Sounds like more than enough for your use. Also I think that if you buy an expensive high end bike you need a cheap one too, that you can lock up for 5 minutes without being scared all the time.
I think for your situation (6 stairs to flat, riding in the park on flat ground) I still think the weight of the bike is ine of the most important things. If it is too heavy you are going to just leave it in the flat. In that case maybe roller skates is better.
I still suggest the Strida or a cheaper copy (ask EvilV). Just take the time to get used to the super cool design!
http://www.youtube.com/watch?v=kVVgsQt1DK4