I like it a lot; just about the only fashionable Irish name that I do like. And I prefer the
Brendan spelling, though my son's best friend since they were three years old spells his name
Brendon.
Bren is inoffensive. It could also be a nn for
Brenda, no doubt, but there aren't that many
Brenda people in the world any more, so that's not an issue.