Richard,
Thanks for the info. After the day I've had at Seacliff looking forward to actual user reports on this filter, then my B/W 77mm will be up for sale.
C
I had a proper go with the Lee today. The foam backing is perfectly intact after four days of the show. It's actually very thin, more like a gasket as MK says, about 1/2mm and 5mm wide. Any problems, they say they'll fix it for you but I don't think that's a worry.
In addition to what I posted earlier, the guy told me they are made for them in Asia by hand and there may be slight batch variations. However, he said it was typically a smidge over ten stops and a little 'cool' but that was the best they could get after a long search.
So I tried it, with white balance locked on tungsten, and took a few snaps of their white display wall, then compared it to my B+W ten stopper. It is very slightly blue, but less blue than the B+W is orange if you follow. Really very minor. A good result I think

I reckon it is 10.5 stops, just like my copy of the B+W. I also liked the way the Lee holder retaining spring-clip pops on and off very easily, so you don't have to slide it in and out and when setting up.
However, while I'm on this obsessive ND thing, I stopped by the Premier-Ink stand and had a fiddle with their brand new variable ND filter - the Light Craft Fader ND 2-8 stops. It works by rotating two polarising filters against eachother. Have to say I was very impressed and bought one on the spot - 77mm for £80. If it's as good as I think it is, that's a bargain and I can see this filter being very popular indeed
It looks well designed and well made, and easy-peezy to use - just rotate it against the engraved scale. Piece of cake to turn it open for setting up, and then down again for shooting. The 77mm version I want was sold out but I'm assured it does not vignette with a 17mm lens on full-frame even though it's thicker than a normal filter, due to the tapered design which is 77mm extending to 82mm outer thread. They supply a nice replacement lens cap, which is good. You can still use a lens hood by fitting the hood first then screwing the filter on second. Should work fine.
Best of all, this was the most netral ND filter I have tried so far. Basically, it's so close to neutral you can forget it. I was concerned about flare, having four uncoated surfaces which doesn't bode well, but pointing it at the bright show lights and doing comparison pictures with and without the filter, well, there was a just-perceptable difference. Need to take a closer look at that but TBH I gave it a pretty good go and it performed well. Bright sun may be different but it was good enough for me to buy one.
I didn't get to check the polarising effect, assuming that it has to have one.
This is it
http://www.premier-ink.co.uk/photog...-craft-workshop-77mm-fader-filter-p-2828.html