Assuming its one of Huawei's newer models I'd expect the API based apps/software to work with it, that is unless EE have customised it heavily and so prevented it. You should be able to test the apps/software just by connecting to it, it wouldn't need a SIM in to do that, just Wifi/ethernet connected to your mobile/pc.
Not sure on the differences.
Is there still data left on the three sim, if so try that, unless its locked of course.
Obviously it won't tell you anything on the mobile network side of things, but you should be able to see if the apps will connect to it and see what they report assuming they doAs always, I am blown away by your knowledge. Never thought to try without a SIM.