Wow this thread really took off and good going finding a local source Alex.
I too intially found this chap through the QHY Site and seems he has made it to APOD and another on SkyantTelescopes editors Choice . So i thought he must to know what is doing, and wanted to look at his equipment list and thats when i found what he was usign for flats. Once i get my act together and get back out there i will certainly be looking at getting one of these.
Have a look at his APOD work
http://apod.nasa.gov/apod/ap081107.html
This was done with a Tokina 300mm f2.8 lens.