Your technique most certainly has merit... I often enter long, get stopped out and flip to a short on the break of a trendline to the downside... in much the same scenario as you describe. I think it is of the utmost import to initiate a position with the trend, since I am a proponent of that old trader's axiom: "thou must trade with the trend"... but once the trend has been violated, your technique is indeed an efficacious proposition, since it now has the laws of probability on its side.