I would NEVER take a polygraph. With a 10% false positive, only a knucklehead would gamble their innocence on one of those!
If you take a polygraph test, you're stupid. If you pass it you're not cleared, and if you fail it, you're toast.
They're not admissible in court because they're not reliable, so you can't flash your winning test as evidence that you're innocent.
In other words, all they can do is make police scrutiny of you even more intense than it already is.
There's no upside whatsoever.