Everybody is doing it, doing it ...
I guess it would be nice if someone did a roundup of all these different implementations, and did some side by side testing, also user experience in the field, etc.
To me, if you need to select magnification to be able to achieve good focus with a certain camera's focus peaking, that's not a great implementation.
Also, don't forget the original focus peaking- unintended shimmering of edges in lower resolution LCD's! This actually worked okay with the Olympus E-P1.