I found two apps, Timegrapher and Watch Accuracy Meter. The second one is free to use and shows beat error as well as error rate. The first one only shows error rate in the free version.
No clue about iOS versions, you're on your own there.
You're probably right, but the "genuine" thing is more than double the price. For me, that's the difference between buying and not buying the thing. Considering the build quality is largely the same, same movement, etc, I opted to roll the dice on the cheaper one. Time will tell.
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