Well, I have used the Wynn's transmission flush machine for years, and have never seen a problem from using it.....
"Wynn's TranServeŽ II+ Automatic Transmission Flush Machine is the first and only transmission flush machine approved by General Motors for use by their dealers! "
http://wynnsforyourcar.com/about_us_5.html
Problem is, people have a problem with their transmission, and most techs "recommend" changing the fluid, and when it doesn't take care of the problem, sometimes the machine gets blamed.......but by then, the cow is already out of the barn....