Sandfire of Kent Spinnaker Staysail

Tim sent in this old picture of Sandfire of Kent carrying a huge spinnaker staysail – tacked onto the inner forestay.

Anyone have any comments on suitability for us?  At the moment, we tend to use our trinquette style staysail for use with the spinnaker, however it is much to heavy to carry at low apparent wind speeds.  Question is – is there any value in building a sail which overlaps to such an extent…