Forum Discussion
Both hardware and software-based modifications are considered cheating if it gives an unfair advantage.
A bigger controller or mods to add more buttons (that simply serve as a single input, etc) should be fine as everyone has their own preference of controllers.
Although I've not got the time to go searching around for the tweet,we have official word from Hideouts that using controller macros such as come with Strike Pack or Cronus is considered cheating and ban worthy.
I would like to point out that, quite pertinent to your exact question, one of the only really obvious tells that an enemy is using such cheats is if they are using a turbo button on weapons set to semi automatic fire with fast firing rates - such as Flatline, R301, Hemlok, P2020. The sound from someone doing this is unmistakable, and will almost assuredly lead to cheating reports from your enemies. Even your team mates will instantly recognize that you are cheating if they are experienced in the game - at the very least you will lose their respect, and they might very well report you just like your enemies. I report every single player I find using such mods, and I know plenty of others who do the same. I also teabag them profusely, mag dump their box, and throw a holo spray on top of it after killing them.
Just don't do it. It's really pathetic when people resort to cheating in a FPS, don't be that dude. Where is the pleasure in winning a gunfight when you know that you won it because of cheating?