Unpopular opinion around here, but IMO, PoE makes sense only for devices with very high bandwidth requirements (like cameras, or APs) whereas Thread is very low bandwidth so there is negligible chance it will saturate your WiFi network. If you have bad WiFi coverage, spend your money on a better APs, not pricey PoE ports for devices that will never use the bandwidth
Keep an eye on posts like this and this about problems with the SMHUB line. This is essentially a Pi Zero-level SBC running Linux so it’s far more complex than the esp32-based GL-S20 which runs embedded FreeRTOS kernel with OTBR. I’m sure SMHUB will get the issues worked out, but the GL-iNet will always be a simpler architecture to maintain — and both are far simpler than trying to run OTBR yourself.
If you don’t already have WiFi 6, my initial recommendation is to upgrade to a WiFi 6 (or better) router with integrated TBR, such as Eero 6 or later. The improvement over WiFi 5 is substantial, and the rest of your network will thank you. These are under $62 (renewed) currently on Amazon and, unlike some other vendors, actually shows you your Thread credentials TLV dataset in their app.