There does seem to be a big difference of opinion as to whether using the bola is a good way to knock in a bat. I have always found it to be an excellent way of getting a bat ready for use in games after work with the mallet. If you watch slow motion footage of a bola ball hitting the blade, it's softness means that the ball flattens on impact, therefore spreading the force of the ball across a wider surface areas, whereas a cricket ball is harder and suffers less compression so that the force of the ball impacts on a smaller area on the blade.
Using a bola frequently will probably impact on the lifespan of a bat though as for a recreational cricketer, you are unlikely to haver the chance to face actual bowlers in the nets anywhere near as often as you can book a net with a bowling machine so you will are far more deliveries in a shorter period of time if you frequent bat against bowling machines