Is roaming free in Finland with my UK or non-EU SIM card?

It depends. Finland is in the EU, so "Roam Like at Home" applies to EU citizens. However, since Brexit, most UK carriers (like O2, Vodafone, Three) have reintroduced daily roaming fees. For travelers from the USA, Canada, or Asia, roaming is definitely not free and can be extremely expensive. A Cellesim Finland eSIM is the cheapest and easiest way to get high-speed data at a fixed, prepaid price.