Quality?
Several members have made excellent recommendations on RAM from vendors other than Apple. I think it's amazing that you can upgrade to 32GB of RAM for only $400. When I purchased my oMP in 2008, I think that price would have purchased 2GB.
I do not have the technical experience to make a RAM qualified statement about the exact (or similar) traits of RAM by 3rd party companies. However, I do know that my local Mac/Apple authorized repair center has noted that on several occasions they've identified the problem as 3rd party RAM.
I bring this up only because I was wondering if anyone else has come across this. If my requirements required the 64GB option, I might consider 3rd party. But at this time, I'm Ok paying the Apple price.