I am not a fan of how they set up the background count. The different levels are completely un-intuitive.
At least with 5e's dumb "+1/+3/+6/+10," it was a modifier each time. The triangular number sequence isn't my first choice for any memorable system, but at least it goes up each time.
And from what I can tell, the effects don't stack, either. If you're at low, you get a -1 penalty. Medium means that edge costs 1 more. High means you can't spend edge. Nothing in the text says that the -1 penalty at low applies at medium or high.
Even if it stacks, you still have to memorize the order. It's just not a very well designed mechanic.
Edit: Ah, Lormyr, you made the same mistake as me- one of the definitions allows you to apply this to any tradition, and the other rule definition only applies it to one.