The danger comes from the keypad, the pop bumper, and the scoop. The lock shot can be backhanded and is relatively safe. The speed of the ball really keeps you on your toes, and the only relatively safe shot is the lock shot, backhanded. I've tried to forehand the lock shot from the left flipper and drained. It's tempting to make that shot as a reaction shot coming out of the left orbit, but I'm telling you, don't do it!
The pop bumper adds a huge element of randomness, and the scoop fires back so quickly that if you blink, you'll miss it and will have to react to get the ball back under control. The inlane/outlane ball saver is another element that can be strategically played to help extend ball times, and I think that's a great touch.
Again, though the ruleset isn't complicated, that doesn't mean the difficulty in progression is not there. It's like playing any 80s/90s video game (IE Mega Man, Mario Bros, etc) where progression is linear, the game isn't super complicated, but still fun as hell. This is what TNA is.