For the past couple of years, I've been using the original Ninja V with a Samsung 860 EVO for 4K recording including ProRes RAW without any issues. When I switched to the Ninja V+, the same SSD worked fine for 8K recording ProRes RAW with the R5. However, something changed recently, and I started getting error messages that the drive was too slow and the unit would stop recording. I'm not sure what changed exactly, but I needed to find a replacement SSD.
Luckily, the first inexpensive replacement I grabbed worked just fine. That's the Samsung 870 EVO. It's much cheaper than AtomX SSDs, and does everything I need it to do. As of the time of this writing, the Atomos website doesn't mention the 870 EVO, but if you're reading this, rest assured - it works!