Informal. No suite, tie, etc. formalities, but at the same time do look & behave somewhat conservatively, this maybe informal but it isn't a "club", either. You will sign profuse, lengthy NDA & NCA (Non-Disclosure/Non-Compete), although technically there's little to worry about, it doesn't hold patents or some seriously inventive stuff. It's just owner's lifetime obsesion with NDA's covering 15-year old designs, FYI Non-Compete is not upheld in many states outside NY, anyway.
Just look carefully at what you sign, because one day you may sign your own death penalty!
The folks there are lovely and lively. Perhaps too much for me...
Only 2 people interview you and is quick ! The company simply has no resources for heavy-duty interviews, you either make it or break it after hiring.
Had to call afterwards, though, to stimulate hiring by showing interest, because I wanted that flex.schedule and atmosphere.