So when using that prop adapter my prop is not going to fall off anymore?
No,it won't provided you tighten it properly.
The 6x5 may be too much for the motor or esc.Could burn either of them out.
Try the standard 5x5 first.If you want to go faster,use the 6x4.
Btw.,using either prop,you will get some plastic rings.Use the one that's a nice fit on the motor shaft,then glue the ring inside the prop with ca.
These rings have been known to come out if not glued in.
Are you going to use the 9x as is,or convert to Frsky?