Hi, my calipers arrived today. Just tried them out (averaging 4 readings - all of which read the same anyway). Got a fat-percentage value of 19.6. Used my Tanita balance and got a fat-percentage of 20.6. I'd say they were reading pretty closely the same and since the calipers cost £3.99 and a flimsy piece of plastic and the balance cost £500 and is a complex, calibrated piece of precision electronics, I'm inclined to believe the balance!
Interesting experiment though.