Pretty happy camper with my New RockPI4 (2GByte):
I had an old but very nice 5 x SATA external case where i had a bananapi running for a long time with a 5-port SATA port multiplexer. Alas with all the problems of a port multiplexer and everything being terribly slow, i was happy when i discovered the RockPI4.
The setup now is RockPI4A with 2GByte memory, with RockPI 4A/B heatsink and ROCK PI 4x - M.2 Extension board v1.4 on which i have an IO 5 Port SATA miniPCIe x4 card to connect the 5 x 8 TB SATA drives. This is mounted internally into the external case. RockPI4A is powered by the cases power supply, had to solder a fitting internal cable.
Debian 9 from radxa wbpage worked out of the box, i am using the eMMC module for the OS. As i have no eMMC/SDcard adapter, i first installed debian onto a microSD card, and in that running system copied the OS img file onto the eMMC (and then removed the microSD).
The eMMC gives me 100MByte/sec read speed and 30 MByte/sec write speed, mode than enough for a snappy NAS, and i do not need to bother with what seems to be more compatibility issues of the nvme board.
The hard drives seems to be working stable with some read/write stress testing over a few days. When i read from all 5 HDD in parallel i get to a total of about 450 MByte/sec. So far i just use JBOD, so no experience with using linux raid5 software so far.
I had/have the following problems:
The heatsink washers where too long, so i had to file/rasp a lot off for the SOC to make contact with the heatsink (described in separate thread, also sent mail to radxa).
I like to idle the hard disks with hd-idle, but when it idles one disk and some other disks have a lot of activity, then the system freezes. I have started to ask in another thread about my option to try newer linux kernels to see if this could be an already fixed kernel driver issue.
The miniPCIe card was USD 50, the AllNet RockPI components ca. USD 70, total USD 120, but of course in reality more because of shipping (if you can wait longer for shipping from china its cheaper ;-). One can argue pricing comparison with small atom solutions, but of course in my case a miniITX would not have fit into the case i have.
So, overall i am a very happy camper with my new rockpi4a NAS.