I have not used it, but note that:

1. Unless you are flying into JFK T4 or T5, you will have to ride the JFK AirTrain to board the Uber Shuttle;

2. If your destination is close to either Grand Central Terminal or Penn Station, the Uber Shuttle -- which is subject to traffic delays -- could well take longer than the combination of the AirTrain and the LIRR to one of those two rail terminals.

Unless you are arriving on a weekday morning, the AirTrain/LIRR combination need only cost $13.50.

If you are arriving at T4 or T5 and prefer the comfort and convenience of a one-seat ride, the Uber Shuttle sounds like a good option.