i have a useful tip, i've seen a sceadu strip out 2 591's on the pitch in 1 days flying and a couple of others go on me while i've been test flying others equipped with them on the pitch, if you read the manual it does say minimum 6kg torque on pitch servo, but i'm not convinced it's just the torque, it's something about the sceadu and the 591 on pitch, they just dont seem to like each other, because after the 2 stripped 591's we fitted a futaba 3001 which only has 3kg torque and i think it's still flying on that servo today, they'll be fine on everything else, just change the pitch one out for something stronger, the jr 8231 would be a good choice.
Generally the 591 is about the best budget servo you can buy, i had over 100 flying hours on my hawk sport with 591's all round and they still worked really good, it's just the gearsets always seem to strip when used on pitch for the sceadu.

Gareth