Do you ever get to practice ejecting out of a plane as a fighter pilot?
Air forces use special training rigs rather than real ejection seats. Example video

Plenty of pilots have survived ejection (Wikipedia says &quot;As of 20 June 2011 ... the number of lives saved by Martin-Baker products was 7,402 from 93 air forces&quot;)
The types of injury are illustrated by this example

The ejection seat has been responsible for saving the lives of thousands of pilots around the world since its introduction in the late 1940s. Typical survival rates quoted in the literature vary from 80–97%.
It is generally accepted that radiographic evidence of vertebral fracture can be found in 30%–70% of aircrew after ejection

The reason real ejection seats are not used is almost certainly the high risk of injury. Ejecting clear from a high speed jet requires a lot of acceleration.