It was experimented live, for real, at the recent club world cup and a penalty decision was made after the referee initially didn't see it.
It's pretty cool stuff, I was sent a whole book by the Scottish Football Association about it and the ways it can change football for the good.
Yeah the thing is, it's not like for every decision, the referee is going to stop the game, run over to his iPad, watch it, think and make a decision. That was only because the referee really wanted to see it for himself and he was probably told to do that to see what affect it had on the game.
For most decisions, as I've read, the guy in the truck will say "yo bro, you missed it, he broke his legs, blow your whistle and send him off now!!" 😂😂
They are still working on it though so don't worry, still very much a work in progress, but from what I've read, the pros outweigh the cons.