the problem with oil flush is that yes it does work it strips all the dirt from the engine but also strips the layer of lubricant off that has been slowly building up on your crank and cams etc... thus leaving your engine in a bad way on the next startup, plus all the crap that gets washed back to the sump doesnt always get drained out as sumps rarely completley empty unless you remove them so you run the risk of the crap blocking your oil strainer on the pump and usually the crap will also block your turbo oil feed , this is rare yes but does happen especially on vw's and audi's
so like above just use cheap oil for half hour or so or just change your oil more often