The major difference is an extra connection between the two VRRP pairs. The fully redundant setup is primarily used in networks that have multiple hops between edge device and core router. For example, consider the simple setup where the pc is connected to an intermediary switch that connects to switch A. Assume the link connecting switch A to the intermediary switch breaks. There is now no path for the pc to get to devices on switch A.
The complex (fully redundant) resolves this behavior by including a connection between the two VRRP switches. Assuming the same simple setup but including the interconnection; if the link connecting intermediary switch to switch A breaks, the pc still has a path to switch A through the backup whereas before it would not if that extra connection was not there.