I don't think any "at home" bodyfat tests are very accurate, but they are accurate within themselves. This means that while you may not know you exact percentage, you can easily monitor change.
The cheap way to go is with calipers. It helps to have someone else use them on you, and I wouldn't worry to much about drastic change in the begiinning since they are not that easy to use and get consitent results. I would do each part at least 3 times to get an average. Calipers are also nice in the sense that you can measure different parts and not just get an overall reading.
Tanita scales are nice. I have like 5 haha. I used to work for them and their product is great. Much better than the dumb one you hold in front of you. If you use the scale at the same time of day, you are likely to get a more accurate reading. I use mine to get an idea, not an exact number. Same with weight, if you eat dinner and weight yourself, then take a shit and weigh yourself you did not just yo-yo diet in one day. For some reason people are willing to accept weight fluctuations but not bodyfat.
I use it and look for trends. When I'm dieting I weight myself only upon awakening and every few days. If I see the numbers generally fall, I'm losing bodyfat. If the generally rise I"m gaining it. Simple as that. Personally I don't care if I have exactly 10 or 12, I want to know if my program is working. I"ll stop my diet when I get the physique I like or the weight I want, not when I hit a certain body fat percentage.