Dave is the stringer material flimsy but light or just plain flimsy?
The reason I ask is that you can obviously live with the fact it is light if you are going to fly, I use 6lb wood for stringers in some builds, which is pretty flimsy. I suppose the problem is the way Guillows supply the strip, most other kits have it in a bundle of mixed stiffnesses so you can select the strip best suited for a particular position in the frame.
From what i have seen The Guillows strip can be heavy but very hard and stiff but still have a good amount of flex without snapping, I've also had some that has been heavy but brittle, like spaghetti. The former is very valuable and useful in other builds as leading edges, longerons and spars....... the other goes in the trash.
Andrew