The following is a short overview what you can expect from small and big H3 devices when used as a NAS. I chose the least capable device (OPi Lite for $12: not even Ethernet and just 512MB DRAM) and the best possible (OPi Plus 2E for $35: GBit Ethernet, 3 USB host ports exposed that do not have to share bandwidth, 2GB DRAM).
I wanted to test also a H3 device in between with 1GB DRAM but since results are somewhat predictable I dropped the whole idea (the performance bottlen