Samsung Galaxy S5 DUOS LTE on T-Mobile

I'm currently looking at getting the Samsung Galaxy S5 DUOS LTE but I'm not sure if it will work well on T-Mobile's network in Washington State. I know T-Mobile uses 1700 MHz & 1900 MHz (3G) and 1700 MHz & 2100 MHz (4G LTE) but do they need both bands or can the phone get by with just a single band for 3G and 4G?

It has the following bands:

•  

  3G UMTS

  B1 (2100 MHz)
  B2 (1900 MHz)
  B5 (850 MHz)
  B8 (900 MHz)

•  

  4G FDD LTE

  B1 (2100 MHz)
  B2 (1900 MHz)
  B3 (1800 MHz)
  B5 (850 MHz)
  B7 (2600 MHz)
  B8 (900 MHz)
  B20 (800 MHz)