Did you read the part which says "micro", these are about 2-3x the size of Pi with those cheap plastic cases. I had mine beside the router before I moved it inside TV console.

Pi will be single purpose device, the "micro" can be full blown server and comes with ALL parts required, no need to hunt for good PSU, case, cooling, storage. Some of them come with 1 Sata and 2x M.2 NVMe, so you can literally pass those NVMe to TrueNAS in proxmox and run full blown NAS with encryption/encoding/decoding in VM.