I find it to be a little addictive, and sometimes find it a bit hard to stop. I always feel like wanting to improve my skills a little more, become a little faster at it, and increase the number of digits I can handle without making a mistake.
The soroban is a great tool for developing concentration, a memory for numbers, a facility for performing a relatively complex series of steps in a certain sequence, and eventually for lightning fast mental arithmetic.
In Japan, soroban use is taught to young kids, who after a while develop enough proficiency not to need the physical device any longer and can perform the calculations on an imaginary soroban, and eventually can achieve some really amazing feats of mental arithmetic, such as this example from their national competitions: 
 - https://en.wikipedia.org/wiki/Soroban
 - https://www.youtube.com/watch?v=Px_hvzYS3_Y
 - https://www.youtube.com/watch?v=7ktpme4xcoQ