The US site says the OnePlus 6T supports

FDD LTE: Band 1/2/3/4/5/7/8/12/13/17/18/ 19/20/25/26/28/29/30/32/66/71
TDD LTE: Band 34/38/39/40/41/46
TD-SCDMA: Band 34/39
UMTS(WCDMA): Band 1/2/4/5/8/9/19
CDMA: BC0/BC1
GSM: 850/900/1800/1900 MHz

That looks like it should be okay here on Vodafone who are 

• 4G - 700MHz (Band 28)
• 4G - 1800MHz (Band 3)
• 4G - 2600MHz (Band 7)

$US549 or about NZ$830 at the moment for 6GB and 128GB RAM and somebody can bring it back for me.

So a pretty good deal.