I have used MIMIX for some years now. The product is good and expensive. It requires daily checks to ensure the replication does not have issues. The software is upgraded fairly regularly, and patches for discovered bugs issued quickly.
The problem is the switchover to the target system. All current operations must be quiesced and there must be no left transaction to replicate before the switch can start. In our environment, this takes approximately 20 to 25 minutes. The switch to the target system takes about 10 minutes, and the subsystems restart on the target another 15 minutes. We test this scenario 3 times a year (we wrote our own CL programs for the switchover and switchback based on Lakeview's templates).
I suggest looking at this thread for more info.