Accuracy (and particularly, consistency/reliability) in scales matters, but you don't need an expensive scale. It just needs to be accurate to a gram (tenth of a gram is better but not necessary) and able to measure up to the weight of your largest batch+brewer+mug/carafe. (1kg should do)

Lots of kitchen scales will work. Coffee-oriented scales also have a timer function which is very handy. Some have more sophisticated functions as well.