Keep in mind (with anything from Aliexpress really)

- will it work on  the network you use ?

- Support / warranty - pretty much non-existent

- Could be a dodgy knock off

- Could be pinged by customs 

- Factory OS/ROM or custom pre-loaded with lots of questionable software

I've only ever had one Aliexpress purchase go wrong, but it was only for a $20 item.

AliExpress in general is quite safe, but I have found disputes increasingly difficult to deal with as AliExpress seems to be siding more with sellers, at least initially. The problem is if they send you a phone, even if it's not exactly as described, they'll just offer you a partial refund. I was almost left with two media players with Rockchip SoCs that couldn't run CoreELEC. The product was described as having a Amlogic SoC which could. AliExpress offered a partial refund because the box worked and the appeal was unsuccessful for the same reason. Only after complaining via their online chat was I given a full refund.

I've reconciled myself to the fact that one day soon AliExpress will not find in favour in one of my disputes and my account will be closed as the result of doing a chargeback with my card provider or for opening too many disputes.

Have bought 4 Xiaomi phones from Aliexpress (Mi2a/Mi A1/Redmi Note 7/Mi 9SE).  All phones arrived ok, the network bands of the Note 7 wasn't in line with the listing (missing b28). 

Be careful of Global ROM's vs Global versions - global ROM means the seller has installed a different ROM to give you the play store etc.  As long as it's a genuine device, you can manually flash official sofware more often than not. I would always recommend Xiaomi.eu roms anyway. 

Think I used goldway for 2 of those phone purchases and the Mi Global Store for the other 2. 

Vrokxx: I might wait to see if the NZ xiaomi store ends up stocking them, otherwise I'll get from that mi global store and I'll have to pay the $150 in customs fees I suppose

Unlikely the K20 range will come here, but the Mi 9T / Mi 9T pro might. The last phone was borderline on the old GST limit, but it was undervalued to avoid this - while I can't gurantee that it'll be the same for you, it's the likely scenario...

Vrokxx: What's the difference between the k20 and 9t, I see they have the same specs but I can't seem to find any actual differences.

Network bands mainly. Mi9T has B28, K20 does not.  

Aliexpress is actually thousands of different sellers with separate Ali stores

Some are really good, some are honestly scum . From experience .
One, Because he didnt have stock , gave me a fake tracking number rather than refund.
Look at the sellers feedback .

Or , NZ Post can loose you package when it gets to NZ , then admit they re-scanned then sent it back to Ch despite NZ Post still having a missing parcel investigation open on the tracking no. From experience .

Bottom line, dont pay any more than you are willing to loose .

Define 'safe'  :-)

Agree with above cautions. I have bought a lot of stuff over the years from Aliexpress, though no phones. Some of it has been excellent value for money, some of it pure rubbish. The problem is, it is almost impossible to tell which is which until you get it, and it is almost impossible to make warranty claims with Aliexpress. I decided long ago never to risk more than a hundred dollars or so with them. It just isn't worth it.

Xiaomi K20 pro here delivered yesterday from ALI. All smooth nothing wrong. CN ROM.  paid $570 6/128gb, carbon black.  18 days waiting time.

Rhapza21:

Xiaomi K20 pro here delivered yesterday from ALI. All smooth nothing wrong. CN ROM.  paid $570 6/128gb, carbon black.  18 days waiting time.

Interslice: I've bought my last two phones from AliExpress, both Xiaomi. Haven't had any issues. Haven't spent more than $400 on either of them though.