The problem is band 38 or 40 isn't supported everywhere. So, I don't't know how good is band 38 or 40.
Since their CS would say use devices that support BAND 5, I think unifi mobile band 5 shall be available everywhere.
BTW, band 5 alone is NOT BAD and could reach 20+mbps.

I think they are expanding coverage with BAND 5, but NOT band 38 or 40.
Definitely you're correct.
Unifi mobile CS and their website FAQs say ONLY use band 5 devices.
So, i think they might adding another "band 5 with 10mhz" as expansion.
Just like Celcom, Celcom has TWO band 3 in my home area, just different 15mhz and 20mhz.