Either the plastic or the wooden prop will do the job. The most important thing is the proper diameter and pitch. Either one will make mincemeat out of a finger or hand but the plastic being somewhat stronger will usully inflict deeper cuts. Wood breaks easier but the damage can still be just as bad. Check the owners manual that comes with the engine for size. Most pilots will soften the trailing edge of all props with a light sanding. This used to be more important when all engines were hand started. With electric starters and chicken sticks you can get away with more.