Better than a bola??
A Bola costs at least a couple of thousand pounds, needs special (expensive) balls, a battery or electricity, setting up and putting away after each use and without an auto feeder requires two people.
It's not got the bowlers arm coming over as a reference to watch the ball out the hand/trigger and is pinpoint accurate, so you can get into position to play a shot early.
A sidearm costs about £20, is easier to carry, can take any balls you already have (or that are cheaper than bola ones) and also needs two people.
You can follow it and trigger as if it were normal bowling, and there's the natural variation you'd get in a match, so it's a more realistic training session in my opinion than the machine.
Both have their advantages and disadvantages, so take your pick!