Striking workers were paid $50 each to skip a day's work and participate in the rally. Since the SEIU is funded by union dues, workers nationwide are effectively subsidizing their own "strike" (hence the quotes).
In NYC, San Francisco, and Oakland, participation was fairly small, in the 100-200 range. In NYC, only one-third of the 150 participants were actual fast-food workers; the remainder were organizers and supporters. This means that only 0.1% (one-tenth of one percent) of Manhattan's 57,000 fast-food workers were there on the street.
As so often happens, the strike may cause more problems down the road for the unions. In Europe, more and more fast-food establishments including McDonald's are moving toward the self-serve kiosk model for ordering. This hasn't taken root here in the US, but it could, soon.
The SEIU and other unions would do better to spend their efforts and members' dollars on methods to match unemployed and underemployed workers with entry-level jobs that have prospects for longer-term growth.