That parting line shows up on one of the three Lee molds I have, and it's the newest mold, a .575. The other two I've had for something like 15-20 years, and have cast thousands of balls through them.
The .575 has just been finicky from day one. I need to carefully close it, then wiggle it a little to insure it's aligned. If I don't do this, there is a "fin" running around it, and even if I cut it off, the balls will end up weighing too much. If I get the mold to align properly, the line is less prominent, which means the ball is potentially a keeper. Near as I can measure, there is about a .002" difference in roundness in the good ones, but that's probably as good as any molds gets, unless luck plays a part.
Lee molds are what they are, a $20 mold. If you take the time to weigh, or even tumble the Lee cast balls, you can end up with some match-grade ammo. It just depends on how picky you are and how much effort you want to put into it. Bill