
I had a vinyl one about 20 years ago. I don't know if the design has changed but mine seemed to get too hot, and after time the pattern of the heating elements inside discoloured the upper vinyl. Didn't trust it any more so it was binned.
I already had a small metal one which I continued to use, and never had any issues with it. I lived in a draughty old Victorian house without central heating in those days, so it was left on 24/7 for my cats while I was out at work all day, and also used for litters of kittens later on.
I've got one out in the garage that hasn't been used for several years, bought second hand for £1 in a charity shop, but I have faith it will be fine if I ever decided to plug it in.