Let me share my experience with the turtle trading method.
I had backtested the turtle trading rules on currencies data. Below are my findings.
If you can follow the rules systematically over a reasonable period of time, you will be profitable. The rules work best or works only when there is a sustainable trend. The method performs badly when the price whips-saw or there is no definite trend.
On average, out of every 10 trades, you can only expect 3 or 4 trades to make the gains. In other words, the 3 or 4 winning trades are going to cover all the losses on the 6 to 7 trades plus profits. Do not expect a high percentage of winning trades using the turtle method.
The turtle method is profitable if you have the patience, adopt a reasonable long time frame and put a trade for every signal that comes along (the moment you get selective, you could miss a trade that is winning). The turtle method is good if you use it on mutiple instruments. In my back-test, I tested it on the 4 major pairs.
What i found for the turtle method is also true for any other trend-following methods. The method is secondary. The key is to adopt a systematic approach with pre-defined stop-loss and take-profit tragets.