It is very cheap but there are some differences between that PC and the usual PCs that you might see on a store shelf. For example, it doesn't use a normal OEM version of Windows 8.1 but rather, it uses something called "Windows 8.1 with Bing". According to ZDNet, prices for this version are probably close to zero for OEMs (
link). It also has a few minor restrictions compared to the normal version of Windows 8.1 and is supported by their Bing search engine.
Secondly, while the processor is an Intel, it is an Atom which is typically found in tablets and mini PCs and runs at a low clock speed (1.33 GHz). Its performance is similar to a high-end Pentium D from nine years ago although obviously it's far more energy efficient.
You can usually find brand-name tablets with Atom processors and running Windows 8.1 at around the same price point as well. For example, there is the HP Stream 7 at $99.99 and the Toshiba Encore Mini at $84.99. If you cracked one of these open, you would probably notice that their internals are very similar.
I'm not very familiar with hard drive mining coins but I know that with BURST, it's usually recommended to go with USB 3.0 if your hard drive is large (i.e. over 1 TB). I went over the specs of the mini PC posted by the OP but couldn't find any mention of whether the USB ports are 2.0 or 3.0.
