FWIW my experience has been good. Just moved into new home that I specifically designed as a smart home.
For me the scope of "smart" is:
After living there for 4 months, I feel the most useful parts of this are:
There are other features I like, but those could mostly be attained with a combination of various retrofit solutions and don't require an integrated home controller like C4.
(C) No other big ones yet, although it did take 6 weeks of life in the house to get things tuned how we wanted. Self-inflicted pain due to desire for some rather complex scenes / automation.
"One Architecture, One OS" also translates as "One Egg, One Basket".