I recommend that if you get a flex fender get the phoenix flex fender, mine have not broken and have been using them for months now and their still strong and solid.
Also make sure that everything is tightened properly and if needed, use lock tight or lock tape so that the thread doesn't become loose again.
Dont tighten your axles 2 tight cause that will screw up your bearings, i just tighten it tight enough so that it doesn't affect the bearings and is tight enough so that it wont wobble around.