I agree that paying for knobs is crazy, for the reasons already stated. For me, i use the turret tapes in that my dope card is my turret. The advantage is the ability to dial out to max effective range without any conversions. The other advantage is in a system that has mismatched retical and turrets. The turret can be mil, moa, iphy, hell it can be in arshins, does not matter as the shooter just dials out to the range required. Work the dope in the off season and save the files. Print them out as needed.
On the off chance someone did want to buy the BDC turret, most come with standard graduation on the bottom, you can see them on the one I posted, rather small but there. So any dope can be dialed in as well.
I use the bdc method because I hunt, in the woods I am at MPBR so i do not need to dial anything, out on the plains is a different story. Hunting antelope in SE Colorado, many times there is no advantage of cover. So the shooter has very limited time to get a bead on the animal. With the dial system it is as simple as Range, Dial, shoot. Comes in handy when your heart is beating out of your chest.