I would probably only use such a thing for basic testing stuff or something. I prefer to build (old and new!) systems into a case because I find that a bit more neat.

Once I get this current build (5600x, 16GB DDR4000, Asus ROG Strix B550, 1tB SN850, 3080 FE with EK silver special block / Alphacool Eisstation 40 / BlackIce Nemesis GTS240 GPU loop in a Louqe Ghost S1 mk3 limestone and reversed L tophat with metacustom spine and zenghost bracket - whew, a mouthful) complete, I'm turning my entire attention to my dual-Deschutes ultimate 1997-1998 build - which cos I don't have an A500 or SR209 yet so will be built on a Streacom BC1. I may even have a go at origami ribbon cabling 😉

Open-air cases are great for testing, but very impractical for long-term use, unless you have over-clocked or runs hot hardware that needs the open-air to stay functional and cooled.

Exactly this. Exposed hardware is a lot more vulnerable to its environment, so I wouldn't even want to ruin it permanently on an open box. For testing purposes I've crippled an old ATX case and use is remains as an improvised test bench, but the name I give it said it all. For testing.

Besides, some people (not me by the way) claim to be physically affected by electrical radiation. If there's one source of electrical radiation, it's a computer motherboard and it's add-on cards. The metal computer case also acts as a Faraday's cage to block the radiation.

I have a retro benchmarking rig set up on a dimastech bench. The motherboard that sees most use on it is my Asrock 4core dual SATA 2, as that can bench AGP, PCI and PCIe. I do occasionally switch out for an ASUS P3B-F with PowerLeap Tualatin adapter to bench/test with ISA sound cards.

RetroGamer4Ever wrote on 2021-08-09, 12:53:

or runs hot hardware that needs the open-air to stay functional and cooled.

So your saying Pentium 4 systems then....

I have more old systems than I can find cases for and what people want to charge for old beige cases its almost cheaper to go with something like a Thermaltake Core P3 TG. Most of my systems are on open air benches (cardboard boxes), I wish I lived closer to a Free Geek but driving 4 hours to the closest one doesnt work.

to be physically affected by electrical radiation.

That's called heat. And yeah, we're all affected by heat.