Band support is the same as stock firmware, since it's set in the modem firmware (that is independent from whatever is running on the router).
this is connected over serial console that means it is limited to 4Mbit/s, it's going to run like absolute garbage for internet access.
It is designed to allow the Raspberry to send/receive SMS or transmit small amounts of data.
Thanks for the warning! Thankfully I held off on that route!
I clicked through the hardware table for ages before I remembered the GL.iNet wifi routers from way back. Sure enough, they have an LTE router too and helpfully, labelled the Spitz series with different regions and corresponding bands.
So I have a GL-X750V2 now with OpenWRT. It's the global version, so supports band 7. The global version, unlike the Asia varient, is cat6, which is even faster too. This should be way quicker than the previous router. Also, a teardown video showed good looking cooling design, even though the router is particularly small. It was, however, 3.5x more expensive than the previous Huawei router.
It's even got bluetooth. No idea what that's for.
I'll update this thread with testing results after I've been using it for a while.
Sadly this router is slow at times too, leading me to think that the speed was just very intermittent and a coincidental with PRESUMABLY busy network times.
It's so hard to diagnose, I'm still not even sure whether b3 vs b7 makes any difference. I was able to get a fast speed on b7 standing outside the building on my phone but when I came in to test the router, it was slow, making me think the signal strength could be the problem. I confirm that my phone is slow indoors too and concluded that it must be the router. But when I went outside to double check I GOT A SLOW SPEED THERE TOO!
It's very frustrating to have speeds changing so quickly that I can't even walk around to compare to configs!
there is also a luci-app (webinterface module) that shows those information in Luci, I don't know if it's in normal repos or you have to install manually, nor if it works with your modem (it should if it's using generic commands as above). https://github.com/koshev-msk/luci-app-modeminfo
So you at least have some actual signal metrics and it's not just black box magic vodoo
This is not uncommon with 3G/LTE/whatever. You probably need to test this at night at weird hours when most (normal) people are asleep if you want a "clean" result.
That is normal - you're in the real world, not laboratory conditions.
In general, the best way to increase your speed is use a modem with higher LTE category. Oversimplification, but think of it like getting a better CPU. The second best way is to use a better antenna appropriate for the location and use case. The third best way (which does not require new hardware) is to band lock to a set of bands that serve your location better. You can optimise these three principles for your budget/application.