The name Steffen pronounced STEF-an is a very strong likable name. Meaning, I think someone named Steffen is someone everyone would want to be friends with, someone you would respect.
It is a very nice name. It may be one of them that people get confused with Stephen from time to time. But I think it is not normally used and unique. I hope to name my son this one day. I say it is a wonderful name!
• https://nl.wiktionary.org/wiki/Steffen (in Dutch)
• https://nl.forvo.com/search/Steffen/nl/ (in Dutch)
• https://youtu.be/q5H_B3ovedE (in Dutch; this bearer is Flemish and the name is said at 0:43 and 0:44)
• https://youtu.be/fgHeAHcA0pk (in Dutch; this bearer is Flemish (from Belgian Limburg) and the name is said at 0:04)
Converted to IPA, it should be: /'stɛ.fən/ [noted -ed]