Umbrella stroller for 15 week old?

Erica

Do you guys think it's ok to use an umbrella stroller like this for my 15 week old son? I live in NYC and getting around has been difficult because most subway stations don't have elevators and buses are tight so I can't bring our normal stroller on either. I wear him a lot but we're planning trips to the zoo, museums, etc. with friends so my son and I would both get uncomfortable using the baby carrier for that long of a time period. He has good head control so I was thinking of an umbrella stroller so i could fold it up on the bus. What do you think?