Yes, it is a very good formula to calculate Pi, but is nowhere near being "the best"!!!. It converges to Pi relatively slowly, at an average of 3-4 decimal places with each iteration. The best formulas used in modern computers to calculate Pi to trillions of digits are the "Ramanujan" formulas of Modular Equations, and in particular, the Chudnovsky Brothers' formula, which gives about 14-15 accurate digits of Pi with each iteration.
