If it's good? It took the world record in calculating Pi, so I'd say Yes, it was good.

> Bellard's formula was discovered by Fabrice Bellard in 1997. It is about 43% faster than the Bailey–Borwein–Plouffe formula (discovered in 1995).

https://en.wikipedia.org/wiki/Bellard%27s_formula

That only works until you run out of resolution in your floating-point representation. When you have to start manually keeping track of digits, that's when things slow down.