There is an overall poor correlation (r = 0.26) between women's self-reported levels of desire and their VPG readings[8] suggesting that vaginal blood flow is not a reliable indicator of female sexual arousal and a better method is needed. Men using the penile plethysmograph have a far greater correlation between reported arousal and blood flow.
See the Wikipedia article on vaginal photoplethysmography. Not the greatest source, I know, but better than the OP's source.
Uh, no thanks.
Not unless I spread out a beach towel, lie on it, and place a container of baby oil next to me.
That’s kind of the point, that many women are simply unaware of or ignore or are not being completely honest about what turns them on. There are a variety of theories about this, but the low correlation is seen as less about the apparatus and more about female psychology.