I bought the 4 x 5kg weights to add to my 20kg York dumbell set bought from Amazon. Just before paying £30 for them on Amazon, however, I checked Argos and found they were available for just under £25. Turns out they've both gone out of stock today so I'm made up I took the plunge and bought them!
It's worth pointing out that the discs do look different to the product picture here (not sure if it's just the lighting though). They are identical in finish to the discs in the afforementioned 20kg York dumbell set. Basically matte black with a slightly rough surface. A small amount of powder-esque substance rubs off at first but a damp cloth will sort this. "York" and "5kg" are cast onto both sides. In my opinion they look pretty tidy as they compliment the chrome dumbell bars I use.
The thickness of the discs is the same as that of the 2.5kg variants: ~ 27mm. I can fit 3 x 5kg discs onto each end of the dumbell with the spinlocks secured. In case you want to know, the diameter of the discs is roughly 190mm. Seems they've manufactured them with a good balance between thickness and diameter. Considering they're made of cast iron, you can slap on a hefty amount of weight without them being overly massive like an equivalent sand-filled disc.
Mine came in a deceptively small cardboard box, which gave the guy at the counter in Argos a shock as he nearly keeled over right in front of me!
Think that covers it; any questions feel free to ask.