Meänkieli split from what became the Torne Valley dialects of Finnish in 1809, when an international border suddenly appeared in the middle of the region. To a Finnish speaker it sounds like a bit old-fashioned dialect, but it's mostly intelligible. It's definitely closer to standard Finnish than Karelian, which takes a lot of effort to understand.

Not so sure. As a native Finnish speaker, I'd say most of us would understand Meänkieli just fine, especially anyone raised on the coastal areas where colloquial Swedish loans are more common in general.