4K Plus has built-in antenna and you could add a secondary indoor antenna to expand your signal coverage directly, no splitter needed. Check the Plus booster panel antenna kit.
4K Smart Link has the standard indoor antenna, and if you need larger signal coverage, you will need a splitter to add a secondary indoor antenna.Check the Smart Link panel and Splitter antenna kit.
4K Plus Pro has the built-in indoor antenna and a secondary indoor antenna included. 4K Plus only has the built-in indoor antenna, and if you need a larger signal coverage, you have to purchase a Plus booster panel antenna kit.
Yes, it will absolutely work. It may not boost the 5g network necessarily, but it will boost everything else 4g and down, and the 5g phone is reverse compatible with the 4g networks.