Well, depends very much of your setup. A “small” to medium setup with HaOS typical runs like on steroids even on this little x86-64 machines. On the other hand arm boards (like the raspberries) sometimes take longer for the HA web ui to load/response. Also the typical arm SBC comes without storage, case or psu and the whole kit often tends to cost more than these little cheap x64-64 boxes which come with everything that’s needed. 
How do you come to this conclusion? Obviously a couple of year old performant laptop which was shipped with a core-i7 probably will outperform such a mini pc with an intel atom or celeron - still they are typical more than good enough for a dedicated HaOS system and typically have a very low power draw -which is something that can make a difference on the long run. 
For example a older but high performance core-i7 system with a theoretical average power draw of 10 watts VS some of this (passive cold and silent) celeron boxes with a assumed average power use of 1 watt. 
Depending on were you live that can be for example something like 30€ VS 3€ annual power costs. 
Still - a old device often is very valid to use and laptops are typical designed for a low power draw and even have “UPS” included thank’s to the battery 
