Screwfix

1/2 isn't necessarily the industry standard. All electric showers sold in Ireland are made in the UK & are sold here in Ireland with 15mm fittings.

You won't be able to use a half inch fitting instead of 15mm but there are no issues with using 15mm compression fittings on half inch pipe.

Having said all of that the answer to your question is that almost of everything sold in Screwfix comes directly from the UK. Most of the Triton & Aqualisa showers don't come through the Irish agents. Screwfix import them themselves from the UK. As a result the Irish agents don't offer any warranty on these showers. The UK warranty is only offered in the UK. You can buy an Aqualisa Aquastream cheaper in Screwfix but it doesn't come with the 3 years warranty that you get with one that comes through the Irish agent.

It's a case of buyer beware