I had the black RAT 7 for two months before returning it, unfortunately I just couldn't get used to it and the sensor didn't always pick up my movements.
After some googling it would see there are a lot of problems with the lack of sensor detection, so be wise before purchasing.
After getting a refund I swiftly moved to a Steelseries Sensei, and i can say 10000% that my aim has improved and it's a much better mouse!
In essence, wait for reviews before purchase to see if this sensor is a bit better!