As a firearms instructor, this is a typical and exercised alternative way to aim and fire your pistol in low light or anytime you can't for whatever reasons use the regular sights. It won't work at long distances with any accuracy, but within 21 feet, and especially closer, is will keep you on target.
Next time you are at the range, try it. Also, make sure you try shooting single-handed with both your strong (dominant) and weak hands.
When I've designed stages for USPSA competition, it is also interesting to see how many people struggle when forced to shoot with their non-dominant weak hand.