I was given a pack of sandford (prismacolor) col-erase
These are erasable prismacolor, they erase quite well however as with other mediums the darker colours do stain, so will need to be taken into account before adding colour etc.
I quite like them, they mean I can happy sketch knowing I can correct any slip ups I may make.
I'm not sure how many layers these pencils will allow , I have 2 layers here and found the pencil slipping in some areas . I used 300gsm smooth card which I can usually get 6 -8 layers on before filling the tooth with pastels an other colour pencils. The lead is quite hard. I think I will use them to sketch only .