That's a great, new option.
But don't forget that on Thursdays and Fridays, it's often possible to get a twelve-hour, one-way rental from Budget from LGA to Manhattan or Brooklyn Heights for $14 or less, with taxes and the first tank of gas included. And, if you have status with AA, you can earn 1,000 or more AA miles for an extra $1.30, or so.
The problem with renting a car at LGA these days is that -- due to the ongoing construction -- the rental-car shuttles operate only to/from Terminal A (the Marine Air Terminal), so getting to the rental-car offices from Terminals B, C, or D currently requires taking two different shuttles.