When I purchased my first Mac Pro, I wasn't aware of 3rd party RAM. When I purchased my second Mac Pro, I knew about it, but had no faith in the RAM. When I purchased my third Mac Pro and was picking it up at the Apple store, the rep said, "we have RAM and can upgrade it and install it for you right now before you leave." I paid for the next RAM upgrade. When I purchased my fourth Mac Pro (B&H), I didn't have to pay taxes so I bumped up the RAM. As I head into the latest Mac Pro, I'm finding I only need 48GB, but 96GB should ensure for several years use. I'm in the "thinking" phase as to which route I will pursue to upgrade the RAM. I know it's the same RAM. And if I buy it from Apple, I haven't and won't have regrets. It's a win-win either way.
Side note: I had a RAM problem on the 3rd Mac Pro. After the Apple store identified the problem, they walked me behind the door to the techs. One of the first things they said to me, "We were all happy to see that you had Apple RAM in your computer. This makes it a lot easier for us. We're going to replace the RAM and since you had to bring it in, we're also going to increase it at no cost."