Devices destined for different regions sometimes have different features enabled/disabled - and may also feature a different Cellular configuration (different bands) for the target region.
For example, FaceTime is not available with any devices sourced from UAE (although this statutory limitation is reportedly now being eased by the UAE Authorities) and some Location Based services are not available to devices purchased in some areas of the Far East. Restrictions are not applied by the location in which they are used - but instead by the country of purchase. To my knowledge, there are no functional restrictions applicable to EU/UK-sourced devices.
You might be best advised to purchase a device in the region where you spend most time - if not from the perspective of functionality, from a warrant standpoint. In the UK, currently considered an EU Member State, you have a two year warranty that is fully honoured throughout the EU. For HK, I don’t have this information to hand - but consider that if invoked, Apple offer a one year international warranty outside of the territory in which it is purchased (NB: some regions may be more restrictive).
Warranty cover is determined by where the device is purchased.