I have not yet found it necessary to do an "engine flush" yet, on any of my cars, but when I have wanted to do a little 'clean-up' (whether it was truly needed or not) I found the 'slow-clean' method was fine.
Either a run or two with a high-detergent oil, or the addition of a bottle or two of MMO, Kreen, etc.. for an OCI, seems to do the trick, and for much less money than what the site the OP listed wants.
... Then again, I've never had an engine that was all sludged up because I never let it get that far.