I'm just in these days focusing myself on this appliance.
It will be a great appliance to migrate data when it will be possible to do it online and overall when it will do a baseline and a final incremental transfer. For whiche I've read up to now is just like another host that avoid you to reconfigure host and application but to online migrate data I still continue to prefer host based method when possibile such LVM. When this is not possible there are no other solutions that "robocopy" or "rsync" the data from old to new.
Read this, a big and recent (2012, may) detailed doc on offline migration using DTA2800