This is actual hardware. Yes simple arm cores can pretty faithfully emulate much of this. But that's emulation. These are bespoke devices, built from actual old chips. Offering a level of comparability and predictability emulation can't always achieve. It isn't for everyone.
Adrian Black ended up with a non functioning unit sent to him by a viewer that bought one. The seller rather than pay for postage for the broken one to be sent back to China just told them to keep it and sent them a replacement instead. Adrian ends up troubleshooting and fixing it but you can get a pretty good look at everything going on inside and some of the old chips involved.