My thoughts? Unnecessary.
Has anyone done it? Probably, you can always find someone to sell snake oil to.
Don't buy one, that's my recommendation.
No they won't drain the battery... Who told you that? And while we're at it, who gave you the idea that you would possibly need one?
Capacitors are a bandaid to fix a broken system that will otherwise fail at some point anyway. If you're not having issues, you have nothing to fix, and therefore nothing to put a bandaid on in the first place.