Do early tests work?

I have a feeling this is the month, I have had cramping, hot flashes, nausea and what I think was implantation cramps (none of these are the norm for me), I am due for my period in 4 days. Does anyone know if the early tests are accurate? They say they can be used six days before your next period, but I don't want to waste my time if they are not accurate. Has anyone has success before their missed period or should I just wait?