These feel quite hit or miss. Many materials hardly look like what they’re trying to represent. Like the metals on the first page (The Metal ---- Scratches) for example, they’re more or less the same thing with different base color, which seems very lazy and the result is sub par with the rest of the marketplace. For the price you’re asking (the same as the whole UE engine) you’d expect top notch quality with perfect material representations.
The site looks nice though, good luck!