I mix a lot of darkroom chemicals at home and have so for a few years now. What I found is
1. Cheap and small scales do not handle repeated darkroom use well. I had two scales, bought on the auction site, that no longer work.
2. You must get a calibration weight and a scale that allows calibration. You'll be surprised at how many off the shelf scales are out of calibration.
3. Secret! You can test your setup using cheap readily available test weights. The coins of most countries have precisely specified weights. For US coin weights check http://www.usmint.gov/about_the_mint...specifications
4. One way to get around a less accurate scale is to make a larger quantity of, say, developer. The requirements for accuracy are much less if you are making 10 liters as opposed to 500ml.
I ended up discussing reliability with a local science supply store and they suggested a cheap model that they had received the least complaints for. Nonetheless, the cheap scales are a good way to start.
I use my wife's Salter digital scale from the kitchen http://www.salterhousewares.com/salt...hen-scale.html. I know she/I didn't pay the listed price. I think I use it more than she does; but don't tell her, I don't think she knows I use it ;-)