As solarvalue has said I wouldn't worry about the quality of the game since it's been made in China. Mike has been designing replacement circuit boards and parts for years. He certainly is a perfectionist.
Some of us have bought his first major build out of the factory which was a Hankin cocktail 60-1 arcade machine. After seeing the Hankin I'm sure Thunderbirds will be built as good (if not better) as any other pinball out there.
The only thing we don't know of course is what it will look/play like and what features/toys it will have etc until it is released.