I never heard of ULA before, and it sounded a bit overwhelming at first. But on a Fritz!Box with recent firmware, it's very easy to enable, and voila! - just works.
Yep! ULA should be thought of as the IPv6 equivalent of RFC 1918 space... with the added bonus that -unlike with IPv4- ULA prefixes are very unlikely to collide, so merging internal networks will very rarely require renumbering.