I used to have an electric de-beaker many years back and used it on the newly hatched chicks. It was fast and painless and the beaks would eventually grow back, but it took a long time.
Now I just use nail clippers and clip back the top beak. Just don't clip the vein in the beak. It does help with those mean and aggressive birds because they cannot get such a tight grip when fighting.
Actually, the beaks can get too long just like your finger nails and some birds need trimming. My breeders seem to have very long beaks and I do trim them a bit if it looks like they need it.
One quail breeder (bobwhite) that I knew used the electric de-beaker and he cut the beaks back to a point that they never grew back correctly. Not sure why he was so aggressive, but he raised 1000's of birds at a time and could not afford to have pecking and fighting problems.
I don't think it is cruel at all if you are careful. It is like trimming a dog or rabbits toenails.