I had a 2017 Focus ST (MK 3.5) that I picked up in Feb 2017 on a 66 plate brand new.
it was a nice car, well equipped and looked great IMO.
Unfortunately the build quality is worse than my 12 year old S3.
I had issues with the Sat Nav locking up and becoming unresponsive, and the built in Android Auto failed to work properly.
Despite Ford running diagnostic tests and finding a fault with the APIM (a known cause of the problems I had) they refused to replace it and claimed a software update would fix it. The update arrived at the end of Jan 2018 and was installed on my car 1 years and 2 days after it was collected. It fixed nothing, the system failed within 5 mins of leaving the dealers!
In the end the car was rejected as they refunded me most of what was paid for the lease over the year, and I bought the S3 instead.
They are known to have failing Bi Xenon headlight units (they go crossed eyed) which is expensive if not under warranty.
Some have reported lacquer peel.
Recaros can come unstitched (some have had this on delivery).
Overall, the car I had was OK and if it didn't have the faults they couldn't rectify I would have kept it, BUT the dealers have no interest in assisting you and Ford UK will pass you from pillar to post until you lose faith in the brand and start looking elsewhere.