Nand flashes often have bad sectors. So those sectors cannot be reprogrammed. In OS they will mark them as bad sector and continue to use it. However as programmer it will not know the algorithm to bypass it To proper way to use it is program the boot (u-boot) and then let the target to program itself. A pure clone will not work if the target has bad sectors.
GQ-5x can be used for backup or data recover purpose. If you want to use programmer to produce clone, then make sure the target has no bad sectors.