Hello
I know theses types of ‘versus’ questions are often not that useful, but I’ll try anyway 
Currently I have a Wetek Play 2 4K (link has spec) with LibreELEC/Kodi installed. It runs fairly well. Bit fiddly to set up Tvheadened, recordings etc. (It seems this device is no longer being supported by Wetek? Though LibreELEC are still updating).
I’m tempted to buy the Vero 4K+, but not sure what will be the real gains (apart from support). I can sell the wetek probably for around £20-25.
Convince me that the Vero 4K+ is worth the purchase in comparison to the Wetek (esp as I have to convince my partner!). I’d appreciate honest answers 
Thanks
The specs are close enough that I doubt your going to get much if any noticeable difference in actual use speed wise. If this box is currently doing what you want and you are needing to justify a purchase I’m not sure what you are hoping to gain by making the switch.
If you plan to watch 4K content, it’s worth keeping in mind that the WeTek uses an old S905 SoC, which means you don’t have HDR or 10-bit output with this chip. This will make 4K content look quite washed out, as HDR output isn’t possible.
Yes, plan to watch 4K in future.
On another note, I was thinking about installing a few linux programmes such as syncthing onto the Vero (which can’t be done on wetek AFAIK). Though is this a practical thing to do or will it compromise the primary operation of Vero?
You should be fine. You have a full Debian system (apt-get). Worst case scenario, you earn yourself a reinstall.