Nothing wrong with nylon gears in many applications. In fact, in smaller models, up to about 60 size, in most applications, nylon gears are going to give you better performance. Metal gears have more backlash than nylon, so the nylon gears will give you a tighter control system. It's only when you start putting enough stress in the control surfaces to strip the nylon gears in flight will metal gears really make sense. (of course, if you crash a lot, you might save money. Nylon gear sets are only $2-$3 each usually, but it still adds up if you crash often enough ).