I interviewed in person in London, I was invited to the office 3 times, I was interviewed by 13 people through 10 rounds. It was a positive experience overall, as you get a taste of their culture. If you are the right candidate, the long process should not be a concern, as lower-quality candidates get filtered out very fast. Managing your own expectations is crucial. People are smart, driven, and genuinely welcome an intellectual debate, which makes it fun.