I was just reading their website and it doesn't give their success or unsuccessful rates....just states that the proven to be "highly accurate". Sounds kind of out in left field to me.
At 8 weeks along, just seems too soon to find out the sex of your baby. Most women have ultrasounds at 18 to 26 weeks to measure baby and some times you can reveal the sex...if baby lets ya! :)
I was lucky to see my twins grow and had ultrasounds every 2 weeks during my pregnancy, but I was high risk. My baby girl showed us once, and my baby boy took 45 minutes to find out what he was. Although I could have had done the amino and definately found out...but we didn't have to go that way since we had a Level II US.
Good luck and don't be discouraged, you will find out soon enough. My one girlfriend has twin boys and is currently pregnant with a little girl. :)
Take care,
God Bless,
J. D