Thanks @cytec for the help! Setting APN via terminal worked immediately
Have discovered you can enter APN details for multiple neworks the same way, it will remember them all, and automatically use the correct one as you switch between sim cards. The webUI will show the incorrect one but it doesn't matter.
Re @mobilebroadband21 question about the UI. Yes it is just broken. However it's the only area of the UI I've found that doesn't work, everything else seems fine, it's snappy to use and changes are applied very quickly.
I've only had it up for 4 days now but it's not fallen over and I've been using it heavily.
You can limit which bands it uses, which is handy, but unfortunately I don't think you can specifiy CA bands. I'm quite new to the world of LTE so I may missunderstand whats possilbe, but for example on O2, by restricting bands I have discovered:
Primary and CA bands both B20
15 down / 25 up
Primary and CA bands both B40
65 down / 6 up
So obviously I'd like it to be using a combination of those, but if I tick 20 and 40, it only ever connects primary and CA to the same bands, never mixed, which honestly I thought was the whole point of CA.
All in all, still happy with it, excellent performance for it's price.
Interesting comparison between routers. So the Huawei CPE Pro is on average a bit quicker, which is what I found, though I was comparing the Huawei B618 with the MikroTik SXT LTE6 kit, RBSXTR&R11E-LTE6
While the mikrotik can aggregate B20+B40 I don't believe it's a combination that O2 have deployed so you'll not see those aggregate together. I think that's mainly because of the difficulties in aggregating a FDD band with a TDD band.