Hi again. Latelly I've been testing some different propellers on my quad and checking the main differences between them. For my emax gt 2218 930kv , my 3S batt and the 1500 / 1600 weight, I was using those cheap 12x4.5 props. I even bought 12 pairs for $25 or so, and one thing I can tell you about them... FORGET ABOUT IT. After 2 crashes from wich I could not tell if it was a motor or prop problem, I decided to test other props. I started thinking that too much flexibility would have a negative impact, both on material resistance after a couple of flights and prop deformation on higher RPMs giving it less efficiency.
Looking close to one of those cheap props with about 3 flights, I noticed the plastic was becoming fragile near the joint to the hub (becoming white as if it was heavily bended). At APC page you can read about the forces involved and afecting a prop, so I decided to start using higher quality and stiffer props, and I'm not regreted.
There are some models wich mix carbon with nylon giving it a good stiffness. I'm using composite APC E series and APC slowfly and also those carbon nylon ones and all seem to behave very well.
One thing you will be noticing is the much quieter noise and less vibration you get from the motors. Balancing is almost unnecessary, and with 12x6 apc e, I managed to get about 2 min. more flying time. So, forget about cheap propellers. I believe they are like tires in a car. If they're not good, you'll crash for shure if you push them.
If you just hover, and don't make sudden alt changes or high pitched maneuvers, the cheap ones will stand, otherwise, get high quality props.