That's what I may end up doing, but one of them will be going back to Thailand and I was hoping to take the "better" one there (as I spend more time there) and leave the no-name Chinese one here in the UK.
CMNET appears to be a China Mobile setting. Would that work on EE network in the UK? I tried it anyway with a variation of Authentification Types but still no good.
It's a PAYG SIM.
I tried the old 3G APN settings from your previous link but no difference (without the IPv4 bit), and the TP-Link article doesn't seem to suggest anything new except it does allude to IPv4 which I was unable to force on my router. Saving APN profiles has been suggested in a couple of places but the router doesn't seem to support that, only making entries followed by "Save and Apply". I've been rebooting after each change too.
SIM card is unlocked.
I may be able to try it in another location next week.
I've also now tried it with my O2 SIM from my phone and it got an internet connection straight away with APN set to "Auto".
That was mentioned in one of your previous links and tried with no success.
This is part of the router interface screen. I think I've been through each setting but no way to force IPv4 as has been suggested in a couple of places. Any suggestions where it could be?
I appreciate the help from everyone.