I upgraded 3 Mac today. The M1 MacBook Pro was on beta already, so it only took 30 minutes and a small download. The two other M1 Mac mini and Intel Mac mini had to be upgraded from Big Sur with the 2.6 ? GB download but the upgrade took less than 50 minutes.
Overall, there is no surprise from my beta experience. However, I was surprised / upset that Bitdefender did not work properly. It blocked the time machine back up. Contacted their tech support only to be told that Bitdefender is not ready for Monterey and sounds look it would not be ready in a hurry