I bought a vintage leather strop at an antique shop. It's got some dark spots, and I can't tell if it's dirt or something like old leather conditioner. Should I use some leather shampoo to clean the strop before I use it?

Also, the strop has a smoother side and a rougher side to the leather. Will the rougher side do the same job that a cloth strop would do?

Cheers,
Michael