only Need to insert an SD card (maximum 256G, recommended 16GB~128GB) to use 

All gradient filters, whether made of glass or plastic, are coated filters. As far as I know, there are no gradients in the glass. Is due to the production of glass. Nevertheless, there are good to very good results with the glass filters. Lee filters are usually made of plastic, with the ordinal number CR39, from which glasses are also made. They are also coated. In fact, they are very good. Due to this complex production, the filters cost a lot of money. And at Lee Filters they are not cheap especially, although they are made out of "plastic", except for the IR filters. They're made of glass. 

It's better to buy a cleaning fluid for lens filter. 

multi-coated layers,different frame thickness and so on. 

I don't see why not, remember that the filter goes on the lens, not on the camera.