They're vinyl not leather.
They work very well and don't affect the paint if:
1. You don't use them all the time (for years) and
2. You clean the insides well before putting it back on and
3. You don't leave it on the car to dry after it gets wet
They're especially beneficial when used on the track.
2008 E92 M3 Silverstone II
2006 MB G500 Gelandewagen Irridium Silver
2006 MB SL500 Irridium Silver (wife's)