I have shot 3 different 6mm lathe turned bullets, but not the G9. They are pricey for sure, and while I would love to shoot them, I have a hard time justifying $1 and up for them when I get good performance for $.23 to $.30 per bullet.
A lighter bullet going faster with a higher BC sure seems like a great idea. Barrel life would likely be reduced (assumption on my part). Performance on game, IMHO is not as good as bonded bullets out at long range. When shooting steel, impacts at long range are harder to see as well.
Do they have merit? In some calibers and circumstances, I think so. For instance, you can get to 6.5 performance levels with a .308 and you can surpass 6mm performance levels with a 6.5. So if a guy hunts with a .308, he can use normal bullets to say 400 yards and then switch to a lathe turned bullet and get another 100 to 150 yards. Or, shooting matches, shoot the .308 out to 600 yards and use the lathe turned bullets for those <20% of the shots past 600. Expand the capability, stick with .308 and have good barrel life. Those are my thoughts.