Yes this is just an unofficial build of lineage os. And yes there will be an official version of it soon. But there will be updates for this build as well. Its completely your choice if you want to flash official version later. But for doing that you might have to erase your phone completely again. That means you will have to change your file system from ext4 ( which is of this ROM ) to f2fs ( which will be of the official version ). That being said , if you want to enjoy nougat goodness and don't mind going through the process of backup and restore - you can go ahead and flash this ROM.