The Troy-Bilt TB575EC is a half crank model, their TB675EC model string trimmer is a full crank. The full crank model has the string pull start on the REAR of the engine whereas the one half crank model has the string pull start on the FRONT of the engine.

I'm no expert on these things but it appears the full crank model is a superior design and perhaps worth the extra $$$$$$......

https://www.bing.com/videos/search?q=troy+bilt+tb675ec+string+trimmer&docid=608019680315638643&mid=15B760B4BEE57A54DC5915B760B4BEE57A54DC59&view=detail&FORM=VIRE