Old laptops as low cost servers? Absolutely, build a homelab in your own basement, rent a cheap VPS, set up wireguard and viola - instant data center for tens of dollars per month. It's not production grade but you'll learn a ton.
But colocation?
Strip away the learning component and add production uptime requirements - why would you even consider using crusty old laptops for this? If you have production grade needs, look to a standard cloud provider or, at the very least, a colo facility where you can put production-grade equipment.
"build a homelab in your own basement, rent a cheap VPS, set up wireguard and viola"
Put an openwrt router in front of your fat server, and for each query it sends a WOL packet to the box, and add some delay to an ethernet bridge.
That was the fat server is mostly sleeping, and only woken up when needed.
I have always dreamed of substituting a really expensive rack of servers with a couple of elderly laptops, with their built in UPS, handy screens, keyboards and trackpads. However, for pet projects, I now have a better way of being cheapskate.
Some ecommerce software stacks really need gargantuan amounts of RAM and CPU, which gets expensive on the cloud. However, it is possible with some software to have everything massively cached, with the cloud doing that, with the origin server in my basement, only accessible from the allowed cache arrangement, therefore having the setup reasonably secure and cheap.
Downsides to this, having customer details in the basement rather than a secure facility, but how many developers have huge customer databases just casually lying around on USB sticks and whatnot? It happens.
They aren't targeting big companies for sure, but maybe a small or medium-sized office could make use of this.