Answer
AS400 high availability software buys continuity, not just another copy of data. It keeps a synchronized secondary environment ready enough that the business can move operations with less downtime than a restore-first plan would allow. The value is in the combination of replication, lag visibility, failover procedure, and test discipline.
Buyers should judge the category by business interruption avoided, not by replication claims alone. If the team cannot monitor the secondary side confidently or switch roles under pressure, the software has not yet delivered real availability.