They’re not inherently compliant… the EST3, for instance, can be used in the UK because it’s available in an EN54-certified version. (There are some operational differences between this version and the original version.)
You can’t simply import a system from across the Atlantic and install it for life safety purposes. Not only would this not be code-compliant, you’d also void the warranty and run into issues with different power supply voltages - and if you’re an authorized distributor and you do this, you’d be in violation of your distributor agreement.