I ran into this with my friend's 16 CX-5. Here's what I found.. Mazda's plugs are much more expensive than the NGK aftermarket. Yes NGK was what was installed at the factory. In the service manual, Mazda talks about making sure the resistance is between a certain value. Why? Because Mazda does something unique in that they use the spark plug as a sensor, it measures the ionic charge inside the combustion chamber. It allows the computer to calculate the performance/efficiency more accurately. All SkyActic engines have this feature and it's not marketing, it's an actual thing.
So that's why the Mazda spark plugs are more money, when most people have tested the factory plugs they're on the lower range of the specification for resistance.
However, no one has discovered any difference when using NGK's aftermarket NGK Laser spark plugs, the resistance I measured was only about 800ohms more than the factory I pulled out. Well within the specified range, since the computer only looks at the difference in ohms inside the combustion chamber. No performance difference when using the aftermarket NGK plugs, and much cheaper!
Conclusion: You're safe using genuine (of course not counterfeit) NGK Laster (platinum side electrode/iridium tipped) spark plugs in your Mazda engine. NGK Laser is the model used from the factory.
Buying from Rockauto I don't do anymore, you could check out NAPA, they have sales when you buy 2 or more items, you'll need 4 plugs so might be not that much more than RockAuto.