I second wouter79's warm Piano World welcome!
Probably not much help, but I have heard of the Gulbransen brand name. In fact, years ago I went to look at an older Gulbransen upright a lady was selling not too far from my home. I saw it listed on Craigslist and was in the mood for another piano project.
I called and made an appointment to go look at. It was in an old farmhouse that belonged to the owner's late mother, and the old Gulbransen belonged to her late mother. The owner, a lady in her 30's/40's (not good at judging a person's age) and her siblings were selling their mother's home as part of an estate sale, and needed to get the piano out of the house.
Anyway, I kind of liked the looks of the piano, and I liked the way it sounded. I took my tuning hammer and rubber mutes and asked if I could check the tightness of a few tuning pins. The lady was accommodating and I tuned a few wayward unisons to get a feel for the tuning pin tightness, which seemed okay.
The piano sounded much better after touching up a few twangy unisons, and I played it a little, and then the lady played it a little and said the tuning I did sounded good. So, I think she was asking like $200 or $250 for the piano, and I offered her $150 (or maybe it was $100?). She said she didn't want to sell the piano for that much. So, I guess I should have left the tuning hammer at home.
I thanked her for showing me the piano and went on my way.
About two weeks later, she called me and said she had decided to accept my offer for the old Gulbransen upright. However, I had already bought another piano project and was no longer interested in the old Gulbransen. (Strike while the iron is hot...
). She seemed a little disappointed but understood.
I did like the old Gulbransen upright, and it was pretty old, but I didn't try to date it... (or even ask for a date:-).
That is about the only experience I have had with the brand. I have read good and bad comments about the brand here on PW over the years. Like many of the brands from the golden era of acoustic piano manufacture, there were lots of different brands, with some manufacturers building multiple brands at the same factory.
The different brand names were probably in the hundreds. Some were better than others, I suppose, but I'm not so sure any of them were absolutely terrible, but my experience is limited.
Not sure this helps, but at least I got to tell one of my many piano adventures... or repeat one I've already told here (sign of gettin old?:-).