Custom Damp is the traditional damp and it block 2 strings and near the bottom cross string.
RVS is difference concept and it block 4 strings and install at the bottom of the string bed.
I have tried Custom Damp & RVS Damp, the Custom Damp is quiet similar the other damper. RVS will absorb the vibrations from string & racquet flame. I suggest you can try RVS, it will give you difference feel (you can find it in HK, around $56).