IF use the real "Sanding Mop" which is from Klingspor, you will need to buy a mandrill and then the grits of fillers you want.
I have a Sanding Mop, it works great and I also have the Mac Mops, they work great also. I think the Mop is more for contoured pieces and the Mac for flat, but for what you want to do, either will work. A little spendy, yes, but like stated, last a long long time.