Concerns re: upgrading to an OWC Aura Pro SSD on my 2015 Macbook Pro 15" retina
You can pick up secondhand Apple OEM cards on sites like eBay very reasonably. I bought a 512Gb Apple card for my 2014 MBP, which has doubled both the original capacity and speed, (as it's a newer 4x PCI lane model).

Alternatively, there are adaptors that allow more generic M2 cards to be used.