Accuracy is poor using the this way of measuring, however, they are good for tracking trends. To get the most out of BF scales is to use them at the same time of day and at similar levels of hydration, stomach contents, and bladder level as all of these factors will change the reading you get.
most are not hugely expensive now, with most modern bathroom scales having the BF function.
I would say yes - when I was losing weight, it was an important factor or atleast for me, but then I used to do this in a hospital, as they have like really professional equipment.