That seems like an easy one to try, though I also wonder on its accuracy. But a spoonful of baking soda in a cup you then pee in isn't really a hardship to try! Gonna go try it.
edit: Mine fizzed a lot. I want a girl, but have been feeling lately like I am pregnant with a boy, so I guess we'll see in a month or so if my baking soda pee (what a phrase...) is accurate.