There are cheap replacement refills but they are available online only. Advisable to buy the original 3M refill also available in Amazon as it lasts 4-5 times of the desi ones and its absorbing capacity is far greater.
Answer to your 1st question is 'yes'. Answer to your 2nd question- i have not used it long enough to need replacement. But I did search for replacable mops and i found a couple on online which said refil for most of the brands. Quality of the product is good.
Fill the water in Scotch Brite Jumper, up to the marking inside, pour liquid, insert the spin mop with round or flat head refill and start mopping,
refer the diagram outside the box, how to use!!! Hope this will resolve your question!!!