CPU on models Fx-22x are indeed quite low power, but my experience is that it is quite adequate for file serving and media serving (including background transcoding) etc. even if it is not really powerful enough for heavyweight encryption.
In general terms, Terramaster units are well built but the Terramaster NAS software does not use ZFS and so the earlier models tend to have limited memory capability.
My F5-221 comes with only 2GB memory as standard and Terramaster offer only a further 4GB upgrade (and this is insufficient for TN Scale). However 8GB upgrade is supported by the hardware and works great, and 10GB is adequate if you are not using VMs and only limited apps.
I wrote this wiki page and indeed most of this section of the wiki precisely because I struggled with deciding what hardware to use.
I chose a commercial NAS appliance simply because I wanted something physically small i.e. not a rack and (although I have the skills to build a box from parts) I didn’t want to have to put in that effort and wanted instead to focus on installing and configuring the software and the learning curve that involved.