The back deck roll is one of the most important technique to turn the kayak to the upright position. The back roll is faster, safer and very easy to learn. Why don't give it a try? You can find here a video tutorial to learn it and understand the technique of this roll.
Who should learn this roll?
It's relatively easy to learn if you have some confidence with your paddle. To perform well in this roll you need to be able to use the blade as a wing on the water. If you are a beginner it's probably a better idea to try the classic forward roll.
Left or right?
This roll can be done either with the left or right blade. However the "right" paddles helps only on the right side working as an helix. With the left blade the paddle makes a lot of friction in the water and tend to sink.
Is it safe?
A definitive answer don't exist. However all the best kayaker in the world are using this kind of roll, because is faster (you reduce the time to hit something) and your body is less exposed to the rocks (because you are less deep in the water). In case of impact, you can protect with your arms rather than hit everything of the head...