So question come up, can you use app's to see maneuvers during tournaments? Or just printed out sheets? Or just ask opponent for dial to show you that's it?

A lot was discussed and said, that only you can ask opponent for dials to show you.

Can you use other stuff?

This all depends on how harsh the TO wants to be because of the "no third party information" rule. If you bring a chart/sheet that shows all of the basics for a ship you should get by with that.

As a TO, since FFG doesn't print out maneuver cards and only has their maneuvers on the packaging itself, I would be fine with players using an app as long as it doesn't slow play down. I am also totally ok with bringing printouts with dials.

FFG OP have stated outright that using a reference for manouevres is OK, though I couldn't provide a link to where. Given that you can always ask to see your opponent's dial anyway when it's not down on the board having picked a move, it seems petty and unnecessary to play otherwise.

I don't have a problem with anyone using the BIG Reference Card.

If I'm remembering right the packaging even says something like 'retain this piece (meaning the maneuver chart' to show your opponent if they ask', so what things a ship can do are supposed to be open common knowledge.

Older tournament rules actually required you to have the insert from the packaging with you for all ships to show your opponent if necessary (though to my knowledge, very few people actually did). I would consider the occasional request to look at one of my dials to be no problem. If it became frequent, and late in planning when that dial was constantly already set, I may get annoyed, but then I'll call the TO over for time wasting.