I've feed over 4000 live prey items since I've kept ball pythons. Not one of my animals has been injured or scarred as a result of feeding live. If I'd had even one injury - that would be .0004% of a chance of injury - extremely low risk.
If fed properly, live feeding is very low risk to your snakes. That being said, feed what works best for you. Buy f/t or use a CO2 chamber if you prefer not to feed live.