[Idea] Smartphone as 2nd Screen+Controller for Games

As far as i remember fallout 4 has this feature but poorly executed.

But i still see great potential

My idea :

I was developing a RPG Games with some very fresh idea. 1 of it,

May using Smartphone AS 2nd Screen + Custom Input.

the 2nd Screen would be like some game in nitendo DS

for input, extra menu, useful info.

How to :

Using Multiplayer Features:

PC = Host

Mobile = Client

Host = main game

Client = Different UI depend on main game status.

My Question :

Any possible Pro / Cons you guys may notice?

especially Cons.

I personally made it work in the past.

There should not be major cons, as long as you make sure the menu interface still is available on the host, in case the mobile cannot connect.

thanks for your reply.