Z wave uses different frequencies in different regions, primarily in order to prevent interference with local mobile phones and ambulance services communications. Indeed, in some countries it is illegal to use a Z wave device on another region’s frequency for just this reason.
Your own devices like sensors and light switches must exactly match the zwave frequency of your hub. This frequency cannot be changed after manufacture.
Some companies, such as Aeotec and Fibaro, Make their devices on both frequencies, so you have to be very careful to select the model which matches your own hub’s frequency. Other companies only manufacture for a particular region.
You can check the official zwave alliance product site to see both the frequencies and the products which have been certified for each region.
If you think of devices as falling into good/better/best categories, ecolink is a “good” brand. Everspring would be a comparable quality on the UK frequency. (But they also manufacture on the US frequency, so read product descriptions carefully.)
Vesternet has a good selection and very helpful technical support: