The power supply probably won’t spin those drives and you may have some difficulty with thermal management. I used a SFF PC case with a SATA extender running outside to a few HDDs for a while. The drives got really hot until I got a fan running over them. This was a super janky setup though. Made a lot of dust. If you’re looking to stay low budget and don’t need RAID or SMART reporting then I would get an enclosure for those drives and just use USB. Otherwise see what you can Frankenstein from what you have. I built a NAS using my janky setup’s HDDs, CPU, and RAM. Got a cheap full size tower, old motherboard off eBay, basic cooler, and power supply for much cheaper than a new build. Still janky but upgradable with a lot of internal space for storage/GPUs.
I love that dock. I had four HDDs in two of these docks connected to one of my servers for a bit. Same experience. A bit slow for large transfers but fast enough for HD streaming. I think the space between the drives allows for enough natural airflow to keep them relatively cool. I think the hottest they got was 63 degrees Celsius during a large transfers. Usually stayed a bit below 60. In my janky homebrew NAS I see temperatures around 50, give or take 5 degrees. The use case should really determine the build so that may be the best option for many, especially with budget constraints.