I ran a test, comparing these to a standard 'whip' wifi antenna, and these are actually worse! The more I look at it, the more I realise I should have known from the start!
The main problem I think is that the driven element is so far out of the plane of the antenna.The boom is also far too wide, and the elements far too thick.
I will see about a mod to put the driven element correctly in the plane. I have two of these and if I dont get them to work im effectively out of pocket by about a tenner (yes, I know its not much for two antennas, and in fairness, the U clamps they came with are probably worth a fiver themselves)
Its a shame, as the little cheapo wifi dongle I bought to improve the laptops connection works quite nicely! Its only about 10dB better than the laptops internal antenna, but since it has an antenna port, it means I can connect a directional antenna to it - If I can get a working one!
I have looked at various homebrew wifi yagis, and will probably make one now and see how it works.
I finally have the spanner for the Larkspur mast! Thanks to Chris G6HTH.
Ive looked around online and made use of a yagi calculator to create a set of dimensions for a 15dBd gain 2.4GHz yagi, using simple materials that I have knocking about. It should take about 2h to knock one up.