It's compact and quite quiet. One word of warning. It doesn't like to finish posting every time. I suspect the PS might not like all the startup current that all 3 HDD spinning up at the same time brings.
There are some entry level Dells I was looking at as well (that also frequently go on sale) but this one won out.
These aren't low power in the same way an ARM-based edge-of-network device might be, but it's been great for what I need: some minimal local services, lots of storage, and fair cpu performance for things like transcoding media.
For a storage NAS, it sounds more powerful than needed. For running hypervisor, VMs and applications, it seems less powerful than needed.
So... I looked at the TruNAS mini before and just configured the base model:
TruNAS Celeron & 8GB RAM (with 1x1TB SSD and 3x2TB HD) vs. HPE Xeon & 16GB RAM (with 1x500GB SSD and 3x1TB HD). So accounting for the smaller drives the TruNAS comes in around 1300USD (>1600CAD) vs the 1120 CAD I spent on the HPE (but I got it on sale).
Note the HPE drive bays are NOT hotswap though they are quick change.
As for VMs, it entirely depends on the workloads you need to run of course. It's lots for mine :) but I can see getting a second one at some point if I needed to.
My next purchase for my rack is definitely going to be an M1 Mac Mini with the RAM upgrade. This way, I can use it as a build server for Mac, Windows, and Linux (the latter two through VMs) + whatever else I want to run. It's somewhat expensive, but it does literally everything I'd ever need out of a home server.
I personally use a Lenovo Tiny M920q purchased used from eBay as a Proxmox node.
Are you doing transcoding or other CPU-heavy tasks? If not, Atom chipsets in laptops will be the lowest power consumption that has significantly more RAM than the Pi 4. If you have CPU-heavy load then Ryzen Zen3 generation are the current winners at performance/Watt.