There are 4 different types of carbon mirrors for the 500, I have had experience with 3 of them.
1. The genuine Abarth 695 ones that cost £600ish, they are amazing quality and inside of the mirror they are exactly the same as the standard mirrors that you have one now.
2. Good quality aftermarket covers that look exactly the same from the outside and have a good thickness. They have a thread glued inside so you fix them by bolting them on. The quality is OK but not as good as the genuine item. They cost around £250
3. The £70 cheap version. This is very thin and had no fixings it is just the outer shell. You need to fix them with a glue. These are a pain to get looking right if you ever can.
4. The ebay ones that go over the covers that you have on now, I have not used or seen these apart from ebay. One thing to remember is that you may well end up paying and extra 20% VAT as they are coming from outside the EU.
I have the good quality aftermarket ones on my 595 now, I did have the genuine ones but got them for an amazing price and sold them for 5 times what I paid. I also had the cheap versions but they were never perfect. Unless you are very happy doing stuff to your car and are happy to take your time I would definitely not recommend these.
TMC buy their mirrors from a company in Italy called youtune IT, you may be able to get them cheaper direct.
Here are my covers on my 595
