Steb offers classes both for absolute beginners and for advanced flyers.
For beginners wondering whether to go to Streb rather than to TSNY (featured in 'Sex in the City' a few years ago): TSNY has a much more glamorous setting (view of the Statue of Liberty) while Streb's rig is inside. Streb is cheaper ($45 instead of $57 to $65). I can vouch for Sterb's staff (many are former TSNY staff).
Streb is convenient to get to: about ten minutes of subway from Union Square (L line), plus a seven minute walk. The neighborhood looks run down but it is very safe (Williamsburg)
For the advanced flyer:
Streb's flying trapeze rig is a little smaller than the standard size, which changes the timing of the swing. On the good side: flying on different rigs teaches you to rely more on proprioception than on timing alone.
The landing net is replaced by a very thick mattress: it is much more comfortable (no risk of rope burn), though much more noisy than a net.
Streb offers individual classes and workshops, sometimes combining flying and trampoline or conditioning. The space is the home of many different aerial artists. There is a wonderful community feeling to it.