Just used this service for the first time.
Once was excellent, the other was not.

The first flight was a J ticket from JFK to South America.
I booked the 5 Star reservation last month because I thought they might be busy during the thanksgiving weekend when we traveled. I didn't have a car booked to take me to the airport at the time, but 5 star told me they would call back a day or two in advance to coordinate/confirm the details and would meet me curbside.
They didn't call two days before, or even one day in advance, and when there were only 4 hours left I called myself to make sure the service was still booked. They told me it was so I told them my car details. While in the car, I heard 5 star call the driver, he asked me if someone was waiting for us, I said yes, apparently they told him to call back when we were closer to the airport. When we got close he tried to call 3 separate times but they did not answer. So when we arrived no one was there, fortunately I took the number from the driver so was able to call the 5 star agent myself. She said she was coming to meet us "as soon as possible." We waited and waited (we were flying EXP on J class anyway, so we could have just checked in ourselves by the time it took for her to show). She did escort us to the front of the line at the JFK F check in, we got our boarding passes and she brought us to security. I assumed we would have some form of expedited security, but she brought us to the regular security line (even if we could have used the premium through our own status...). The line was not long, so we waited, but it seemed bizarre.
She told us she would meet us on the other side in the lounge. I thought this was strange because if we didn't have elite access to the lounge ourselves already, we would have had no way to enter without her. We went to the lounge and she came and found us 15 minutes later. Then when we heard an announcement that our flight was boarding she was again no were to be found. By the time she came back to us in the lounge and we got to the gate, they were already boarding Y and we didn't preboard.


However, the return flight was a completely different story.
When we arrived from at JFK there was an onboard announcement with my name to see the agent on the jet bridge. A pleasant agent was waiting to escort us. She took us to the front of the customs line and we breezed through security. She even escorted us all the way to the taxi line and saw us off. This agent was clearly more experienced and an excellent representative of what this service could be.

Overall, I don't see the value of the service for anyone who flies enough to know the system on their own. Perhaps if you have no status and don't already have priority boarding/check in this makes sense (although in my first experience, even this was not guaranteed), or if you are traveling during a heavy traffic time and need to land and get through customs quick, it may be worth it. Otherwise, the price is steep for essentially no real service provided.