This might sound ugly but with the same type of failure on tow different props that are NOT systematic of just "flying apart", this looks more like a "user error" than a material defect. 
We don't know if there is/was any stress during transport, storage, shipping, or handling. 
Also, knowledge of how that large missing section got there when the post leads us to believe the prop disintegrated in midair and should have been static/still at landing (dead stick)?
Do you hang the planes by the prop when not flying?  Is there any stress on the props at storage and are then stored indoors or in subfreeze garage conditions?
Just for heck of it, when you install new props, give them a light flex motion prior to startup just to check and see if that movement causes them to break?
Make sure your spinners are not biting into the prop?
Perhaps leave the glow plug OFF and give them a few normal starting attempts, then disassemble the spinner and closely examine the prop PLUS give them a good tug, pull, flex and see if they break  (I'm not saying bend them until they break)
Just a few suggestions and ideas.  Typically, one sees this type of failure due to prop strikes and I will venture to say that they just don't self destruct under normal usage.