IBM aquired Datamirror some years ago, then in 2012 IBM sold the ex-Datamiror product portfolio (iCluster) to RocketSoftware.
As far as logical replication HA solutions are concerned my impression is that the leader is Vision Solutions (who aquired Lakeview Solutions some years ago) with MIMIX both in terms of market share and in terms of solution and support quality, and in terms of being a visionary for logical replication HA solutions.
Our HA consultants have had experience both with iCluster and MIMIX products and their input thus far suggests that while iCluster is a fairly good HA choice, MIMIX Availability product line is superior when it comes to ease of use, functionality, reliability, customer support and consultant network. We have quite a few customers using MIMIX running heavy transaction workloads, and switchover time is no more than a couple of minutes. We also have customers with iCluster, but they are now thinking of returning to MIMIX.
There are of course other, hardware-based (and OS/400-based) HA solutions for iSeries (e.g. PowerHA SystemMirror) that are definitely worth considering, since over the years these hardware-based solutions have become more and more enhanced. Hardware-based HA solutions can be configured and managed somewhat simpler than logical HA replication solutions, but these may lack useful features logical replications do have (e.g. selective data replication).
Your best HA choice basically depends on multiple factors such as your current operations environment (amount of data to be replicated / change rate, distance and bandwidth between backup and production site), your existing hardware infrastructure (e.g. do you already have some kind of external storage?), existing skills of your staff and your Recovery Point Objective and Recovery Time Objective.