Break cues are kind of like the flavor of the month.
One says use a lighter cue to get more speed.
Another claims more weight will aid in putting more force into it.
Stiff shaft.
Phenolic tip
Large diameter tip
Small diameter tip
Then it gets into kicking up your leg and moving your body forward.
Basically it come down to what you are comfortable with to have control.
I will use my playing cue, don't hit that hard but as hard as I can to keep control. I usually make balls on the break and many times the game ball. I get better results doing it way than those that hit as hard as they can, miss the target, scratch or have the CB fly off the table.
I am not a pro as most aren't. To get results like the pros you need to practice break shots for hours and then fine tune it by experimenting with break cues. The break cue will not automatically make you better at breaking
It also depends on the game you are playing.
So what makes a break cue? The player, the game they are playing and for the majority of us bangers looking for the magic feather or wand, marketing and hype. Best is to use what you can control.