I currently have two problems with this:
* While looking backwards, I do not see where I am going. 
* It is difficult to maintain perfectly the same direction while turning around. 
Probably both problems can be fixed by training on a safe place, but is this way of looking backwards a recommended and safe technique? Maybe better to avoid this? Or the clue is to learn returning back to the forward view very quickly?

The obvious alternatives are:
* If only another another bicycle may be approaching from behind, just show the hand signal  to understand which side to drive around you.
* If you make something like a left turn across a car road, stop to look around.
* Engine noise (and lights in the night) from behind can warn about the approaching car.

There are also other options now like mirrors <strike>(I tried some so far without obvious success)</strike> good mirrors make sense and Garmin radar (not cheap). Anyway this question asks is it worth learning to look backwards while riding or better to learn avoiding this habit?