I run both and I'm confused as to why you would need OpenFiler. They both use essentially the same underlying technology. (And the same iSCSI target (IET))
If you need to tweak the Thecus further, you can easily add SSH access to it and customize the iSCSI settings to meet your need. OpenFiler much better about iSCSi other than you have more flexibility about the size of the iSCSI LUNs you create.