You are correct, they are a pain to clean. After a blast with a pressure washer the black parts remained dirty. Next time I cleaned them, I gave them a good brushing with a proper wheel brush and soapy water after loosening the dirt with a pressure washer and still dirt remained on the black parts. I ended up on my knees with a sponge and soapy water to get them clean.
I expected them to be fiddly to clean. but I didn't expect the dirt to cling on so well.
As the weather gets warmer now, I will give them a good clean, after which I'll coat them with a product that will stop the dirt clinging on so well. I haven't decided what to use yet, so any suggestions for a suitable product would be welcome.
As for the mats, they are not standard. MIne were given free with the deal, but annoyingly, I wanted rubber ones and I was told that Hyundai don't supply them.