Why the fifty old destroyers were a separate bargain

Were the fifty American four-stack destroyers part of Lend-Lease, and were they worth refitting?

They came through a separate bases-for-ships agreement and were useful because Britain urgently needed convoy escorts before new construction could arrive.

Britain exchanged long leases and base rights for fifty American destroyers under an agreement separate from Lend-Lease. New escorts and reconditioned British ships could not arrive quickly enough after losses that included eleven destroyers in eleven days. Whatever their refit costs, the transferred hulls could be put to convoy work during the immediate emergency. The American bases also strengthened Atlantic approaches and contributed to Canadian as well as United States security.