I found these quite interesting, but I'd never get one implanted: using small screwdrivers and wrenches would be a pain, it affects the phone's magnetometer and you have to be careful not to cut your finger or when lifting anything heavy (and using all your fingers' strength)...
I've had no issues with screwdrivers or wrenches, it doesn't affect my iPhone at all (I've brushed that finger over every inch of that device trying to feel inside it) and it was surprisingly easy to adjust the way I carry heavy things.
