Is Abacus/Mental Arithmetic good?

I teach abacus/mental arithmetic and I'm always asked, is it good?

Yes, I would answer "It is good because you'll learn to handle big problems fast with good guessess, within a certain percentage of error or so".

You'll learn to do arithmetic fast, in that way you can spend your time thinking about what the numbers mean. Use that rapid arithmetic skill in the examination battlefield and you know you have the right weapon.

But, I must warn you. Learning abacus is boring. It involves plenty of calculation. It requires persistency and consistency as well as patience to practice daily. Once you stop training your brain, your brain function will begin to decline slowly again.

So to learn or not to learn? That is the question.
Well.... abacus is not the only aid in town. There are other methods on brain training, flash memory. Again, once you stop, memory fades away.
But because abacus/mental arithmetic requires you to calculate sums quickly, it activates the largest region of the brain. Your prefrontal cortex is actively working.

Preforontal cortex = frontal lobe (also known as motor function - foundation of creativity, memory, communication, and self-control).

 Putting aside this medical term and scientific research, my humble thoughts is that once kids achieve good mental calculation skill, they will attain confidence in exam and self-esteem in their life skill.