so in choosing between these two (i am not considering the bm818-a1) the big question is: how important is the 1 band only supported by the bm818-e1 (lte-fdd b20 800 mhz) vs the 7 bands only supported by the bm818-t1? some mobile phone providers in some european countries (it seems only small countries) use only lte-fdd b20, but it seems in most of these countries there is another provider that uses another band. what countries can you get service in with the bm818-e1 that you can’t with the bm818-t1 and vice versa?
ADDED LATER: i should have been more clear. what i’m wondering about is which modem gives a larger region in which you can always find a mobile phone service that works with it. the lte-fdd b20 band is heavily used in europe, but it seems that there is nearly always another band available, so it seems that only a very small part of europe would not be covered. would the 7 additional bands offered by the bm818-t1 cover a significant number of countries in asia? is this the most roaming friendly modem?
You could also take into account that the modem is not hugely expensive. So if you live in country A right now and choose the modem that is best for that country and then some years down the track you move to country B and the other modem would be best there … then you can buy the other modem, or buy it now.
Changing the modem is far from ideal on an ongoing basis i.e. would not be an appropriate approach if you are going on an around-the-world tour, but it should cover you for the occasional international migration.
Looking only at countries is only part of the issue though. You really need to look also at individual carriers. If you end up being forced to use the expensive, dominant, legacy carrier because of your choice of modem then that choice of modem may be false economy.
Looking only at carriers is only part of the issue though. You also have to look at the specific places within the country that you want to use the carrier. A carrier may use multiple frequencies in the country but there will be some towers where the carrier uses a single frequency.
For true wanderers I hope that one day Purism is able to offer a modem that supports all the LTE bands (but this is of course dependent on the modem supplier producing such a modem).