It's located right next the the new york police department which is the largest police department in the US with 38,000 officers [0].
It is also located right next to the courthouse and this is the procedure to go to court:
In an article published on April 5, 2011, Jim Dwyer of the New York Times described the experience of an inmate being transferred from the facility to the federal court across the street: A prisoner going to court from the Metropolitan Correctional Center is presented to federal marshals in the basement of the building. Shackled at the ankles, chained at the waist and cuffed at the hands, the prisoner hop-marches through a tunnel nearly 40 feet (12 meters) below the street. The prisoner and escorts go through channels, or corridors, with electronic doors at each end. These are controlled remotely by officers who watch the journey through cameras. More prominent prisoners, who need to be segregated from the general prison population, are housed in the 10-South wing, which is noted for severely confining conditions.
During this passage from jail to court, no one lays eyes on the prisoner except the marshals and the people in the surveillance stations. Once they have reached the north end of the tunnel, they wait for the prisoner elevator. Inside is a locked cage that the prisoner stands in for the ride up to the courthouse cells [1].
I think it is pretty secure.
[0]: https://en.wikipedia.org/wiki/New_York_City_Police_Departmen...
[1]: https://en.wikipedia.org/wiki/Metropolitan_Correctional_Cent...