The secondary address exists so that a problem with the primary never takes Awazon out of reach. Every address in the pool resolves to the same market with the same account, balance and order history, so switching from one to another costs you nothing but a fresh Tor circuit. When the primary is slow, this is the address to move to.
Availability over the window sits just under the primary, in the high ninety-eight percent range. The small gap is not a reliability concern. It reflects the primary catching slightly more traffic and therefore slightly more of the routine checks that happen to land during a queue. Both addresses are equally genuine and equally safe once verified.
Latency reads low to medium. On a good circuit it is indistinguishable from the primary. Under a coordinated flood it may queue a little longer, which is expected behaviour and the reason the pool has more than one address in the first place.
The verification rule does not change between addresses. A secondary is not a lesser address that earns less scrutiny. Verify it the same way, every session. See verifying a mirror.