I have one that I swap between my 30-06, 25-06 and 223. But, I invariably dial the turrets if time permits. Otherwise, I have a cheat sheet taped to my rifle just in case I roll up on a pack of wild hogs and have to act quickly.
How "accurate?"
For starters, the BDC reticle has thick lines and the circles are large. So, it's really difficult to do precision work which goes against the grain of "aim small, miss small."
However, there are a number of good reference points that you can use for quick shots and that's what it's basically intended for. But, only you can determine how well that works based on practice.
Like Vette says, you can use their website tool to help figure out your drops relative to the reticle. But, you ultimately have to go shoot it.
I'm thinking that the 270WSM is pretty flat out past 300 for coyote. (hold hair, or just over) After that, you may be somewhere in the first circle at 350-400 and then around the second circle at 500yds.
So, back to my earlier point. The circles are large and don't provide for fine aiming points at longer distances which is when your target really begins to shrink.
Ultimately, I'd much rather shoot the rifle and make note of the reference points and yardages than dial my power down in order to have the reticle subtend more closely to my trajectory curve as suggested by the mfg.
JMHO
--richard