TIK files are around 2-3KB, so they can easily be downloaded and transferred between consoles. You install them to your NAND (ticket.db) which takes less than a second, and then you can download the software from the eShop for free. You can download multiple things at the same time, and it wont require twice the installation space. It works in sleep mode, too. Also, sinece the data is coming from nintendo, theres no chance of the game bricking you.
CIAs are big, require twice the insdtallation space, take a long time to install, and only 1 can be done at a time. And there's also a chance the game could not work since its coming from a random guy.