It sounds a lot like the vowel in "bird" in English, or like the vowel in "schön" in German. I think the proper phonetic letter for the Finnish ö is a bit different than in English and German and because we (I'm a native Finn) only have like one version of each vowel, I actually find it really hard to hear and especially imitate the other phones which is why I might pronounce them slightly "wronly" when I speak English or pronounce German - I just don't hear myself because the difference is so small, so I hope I'm getting this correct here :)
I think you're right. I was trying to find an equivalent that you might hear in Britain. As an English speaker, the ö in söpö sounds very like the vowel in fur, bird, occur (south east UK, without the rhotic American R ending), or like a slightly extended schwa. In fact, I think it sounds more "open" (with very slack lip rounding: no "pursing") than the French peu or sœur, or the German schön or Österreich.