There are three Magics at our club which have all been flying all summer.
My Magic is using Futaba S148's.
The second Magic is using the same.
The third Magic is using Futaba S3003's.
None of us has had a servo failure yet. Nor have I read any posts where anyone has had a servo failure using standard servos in a Magic.
IMHO The JR537's should be fine.
Enjoy the Magic. Your going to have fun!