Purchasing a Chinese phone query

fabfivefreddy

Help please!

I'm looking at a couple of Chinese phones - Oneplus 6T and the Xiaomi Mi 9. I'm happy to buy online from non high street companies but unsure what does and doesn't work in the UK.
I've spoken to a seller about a Oneplus phone and he has told me the following: it is the Chinese version but has global ROM. It has google play pre-installed and the Oxygen OS.
I've tried to google all the above and establish whether this is good for the UK but I end up running round in circles and unsure if I should buy this or not.
Some advice would be great? I appreciate that if I purchase this the customer support would probably not be there. More interested in whether this is usable out of the box and any pitfalls I would have moving forward.
Thanks in advance

Hixs

Global ROM means it'll work in the UK.