I purchased the Cokin filters to get me started with using ND grads as I didn't want to pay to much money, but I found them to be anything but neutral.
Although they were not as bad if using them individually, when stacked they gave a very strong dark purple colour cast and some vignetting at the edges.
I then tried using just one of the 1 stop ND grad filters and my B+W 10 stop filter and the purple still remained.
Even when I took a picture of a stormy blue sky and adjusted my white balance in camera to compensate and used only 1 filter, the picture still came out purple, so I sent them back and will be saving up for a set of lee filters instead.
On the plus side though, if you really are on a budget and you can live with the colour cast, the build quality of the holder was quite good and the filters themselves were OK apart from a few chips on the edges, but this couldn't be seen in the image, then these might be good to learn with.
Each filter was supplied in its own hard plastic case, which gave ample protection.
You might be able to adjust the colour cast in your editing software and I had some success with this, but for me I want to get as much as possible right in camera and do as little as I can in post production.
So to conclude, if you are only ever using 1 ND grad filter then you might be OK, just be aware that when using a polariser, an ND grad, or stacking the ND grads together, a strong colour cast might be apparent, my advice would still be to save your money and buy something that is truly neutral.
(I used these with a Nikon D7000 + 18-105mm kit lens)