I got a comment that the "H&Y Fader ND" is an imitation from the "Light Craft Workshop fader". To be honest, I have no clue which one is the original, but I think it's the "Singh Ray Vari ND" because this is the most expensive. I read Phillip Boom's post on these faders (this is the post) and decided to get the cheap one. I paid $79,19 (=64,42€, ebay seller "anne14389", shipping took 2 weeks to Germany) for my 72mm sized filter. I think this prize is unbeatable. But as I said before, I don't know if this is a genuine filter.
Here's a sample video of the H&Y Fader ND on my Canon 550D with a EF 50mm 1.8 II lens. The setting was 1080, 24p, 1/50s, f/1.8, ISO100 and I twisted the fader from it's minimum to the 8th stroke (the maximum is on the 10th). It was really really bright when I shot the video. I had to choose f/20.0 to get the same image without the fader. By the way, the colors are flat because of my camera setting.
The thread on the outer side (e.g. for a lens hood) is 77mm. Build quality is really good (metal and glass) and the box it comes with is also really nice. Only negative thing so far: it doesn't come with a lens cap so you have to get one seperately. I ordered one for 5,98€ on ebay. I also ordered a 3 way rubber lens hood for 4,45€ to avoid lens flares and to protect the fader.
I will use this fader with my EF-S 18-55mm kit lens and with my EF 50mm prime lens. The kit lens has a 58mm filter thread, the 50mm prime has a 52mm thread. So I ordered 2 stepping rings (each one less than $2 on ebay) which make it possible to thread the Fader ND to these lenses. I decided to buy a bigger fader because I want to use it with lenses I will get in the future, too.
What are these faders used for? They make it possible to darken the image like normal ND filters. The only difference is that you can adjust the density of the filter (range from ND2 up to ND400 with this fader). This makes it possible to shoot videos with a wide open lens in bright sunlight without changing the shutter speed. Another nice thing that you can do with these faders is to take a long exposure picture in bright sunlight without getting it overexposed. This is a nice technique to shoot a sight on a crowded place if you don't have the chance to shoot it without people in front of it - the people will be blurred and you can see the whole sight. Another thing that many people do with this type of filter is to shoot water with longer exposures to make it look smooth.
What can I say about the optical quality? I think it's great. Colors are nice and I can't see any distortion or vignetting at all. Only when I twist the fader over it's maximum - but this is not what it is supposed to do. I will use this filter for shooting videos primarily, but it also works nice for taking photos.
If you want a really cheap Fader, get this one. Maybe the more expensive faders will give you even better quality, but the price-performance ratio of the H&Y fader is excellent for people on a very tight budget. My rating: 5/5.