You'll need to be doing a lot more than just 100km/h for the thing to be even remotely effective. You don't even begin to work the rear wing until at least 160km/h.
In marketing language, a gimmick is a unique or quirky special feature that makes something "stand out" from its contemporaries. However, the special feature is typically thought to be of little relevance or use. Thus, a gimmick is a special feature for the sake of having a special feature.
Something like the your 'magnetic fuel conditioner' isn't a gimmick, that's downright fraud.