I had an Early 2013 15-inch MBP which is essentially the same architecture as the 2012 models and I used an adapter similar to this adapter pictured below
and I purchased an SSD similar to the one pictured below with no issue
Personally, I avoid OWC RAM because I feel you are overpaying for a product that is not as fast as others that are out there. I have always used Samsung drives in my laptops. Never had any issue using these storage drives.
Since the 2012 and Early 2013 MacBook Pros use Sata III instead of NVMe M.2, this was the way to go for me. There are more limitations when having to use SATA III as opposed to NVMe M.2 but there are still better solutions other than having to use OWC in my opinion.
Anyway . . . . let's get back on topic . . . .