I purchased my Samsung Note 20 Ultra 5G from WondaMobile because I wanted the Snapdragon Soc instead of the Exynos soc that Samsung UK supply.
WondaMobile is a trusted site I prefer to use and have good reviews on TrustPilot.
No import fee's and they supply the Hong Kong variant.
I sent the N20 Ultra 5G Exynos back to Samsung UK for a refund.
The difference in my opinion is night and day in regards to the two different phone's especially with how better the Snapdragon version is at optimisation.
I've had no issues @Jaskey with this phone ( touch wood ) at all.
It holds onto signal better too.
However as I'm on UK Payg type accounts I've been unable to see if 5G works. Some on xdadevelopers.com say it does.
You'd need to check what 5G bands and frequencies your network uses to that of what the phone supports.
As far as I'm aware all other calling features work as they should, however I don't think voLTE does.
The Samsung Keyboard is slightly laid out differently, but a person can use a downloadable option if preffered.
I use Vodafone and o2.
I also use Google Pay without issues as I don't use Samsung Pay. Samsung Pay may not work.
The phone receives software and security patche updates as normal.
eSims are not currently supported.
As for warranty it's true that Samsung Uk may decline support but I've yet to test this out, although hopefully I don't have to as the phone is still going strong.
That said if I did and my local Samsung Experience Store or Samsung Service Centre declined support then WondaMobile apply their own 12 month warranty, and arrange to collect the phone.
I also have my phone's covered under my Home Contents Insurance.
The phone came sealed and fully unlocked to all networks, with no region lock applied either.
Hope that helps but if you have any more questions don't hesitate to ask. 
