Mary Malmros wrote:
...and then, after you've been diagnosed with tennis elbow...
… you learn the proper stretches, exercises, and massage techniques that alleviate it. Or you could just start doing that now.
The way I view sledge hammer training is not so much to build arm strength, but rather explosive hip flexion and torso rotation, and of course, your grip will be tested.
That said, Mary makes a good point. All training should be done with an eye towards your specific goals. I don't think sledge hammers should replace bokken and suburito. However, if used intelligently, they can compliment your training (much like bokken training does for katana).
And frankly, swords cut pretty easily.