Piggyback ECUs (Racehip etc) - are they detectable?

[Beethree]

Fairly random question but something that I've wondered as I see it mentioned on forums/groups alot, are piggyback ECUs such as Racechip detectable by manufacturer diagnostic systems once removed?
I often see that they aren't (the sellers usually promoting this!) but I would have thought to increase power they must have to increase fuel and/or boost and that this would be logged somewhere as reading outside of the manufacturer tolerances?

Does anyone have any real world knowledge/experience on this?