After a $10 activation fee, get 20 rides at those flat rates within NYC (airports excluded), or pay $20 for 40 rides within 30 days.
Effectively, it is $3.49 per Uber Pool ride, or $6.49 per Uber X ride.
Map of included areas is here
Sign up is here
"Flat fares apply to rides up to a $30 value for uberPOOL or a $30 value on uberX (based on time and distance). If your total ride cost exceeds the maximum value, you’ll be charged the flat fare, plus an overage for the dollar amount over the maximum ride value covered. And don’t worry, if the total ride cost is ever less than the flat fare, we’ll charge you the lesser amount."