How can i make sure this works? Should i see the locomotives flip orientation? Does engine smoke comes out of the (theoretically inactive) locomotive?

You should visibly see the back locomotive rotate to face the direction the train is going and help with acceleration.

Then it means it doesn't work for me. Does it only work for a particular layout of locomotives? Or it rotates any locomotive connected to a train to face the right direction?

It only works on dual header trains (with locomotives facing both forward and backwards, the number and in what arrangement is irrelevant) and their schedule needs to be set to automatic.

Oooh, then that's why i couldn't get it to work! lol, i was testing it in manual. Maybe you should mention this in the description.

Alright I can do that. Thanks.