Isn't it more about effectivness of a kick ?
Sometimes when I am doing Randori or soft Kumite I am thinking about which techniques can be used.
Usually I have much bigger partners (taller, heavier) and they would laugh about my Mawashi-Geri (although I don't think that I have a weak kick). But when I look at their faces they would "take" the Mawashi and send me to the floor. Ok ... you can kick it on Solar-Plexus height ... but it don't works every time.
The same with an Ura-Mawashi-Geri ... would I really use this kick in Randori or Kumite ? I guess not ... I have to be too fast and in most cases you can see what your opponent is doing.
I think Mae-Geri (Kekomi and Keage) can be very effective ... and Ushiro- Geri as well in a fight.
In general I try to train every kick ... and improve technique ... but how do you define difficult?
Is it really about technique-difficulties or more about difficulies in effectiveness?
Good points Gungnir.
I made a similar comment earlier about effectiveness versus technical correctness to Azzy so I guess it's obviously one are for discussion - any thoughts anyone or do we need to split this of for another topic ?
Regarding effectiveness of  Mawashi/Ura-Mawashi - I've never seen any comparitive studies on the frelative forces generated by different kicks but I would agree that the overall force/impact generated by an ura-mawashi would be less than say a yoko-kekomi.
However in kumite it's sometimes worth recognizing - IMO - that teher acn be differing levels of effectiveness that are most appropriate for different circumstances.
What I mean by this is that it may be more effective overall to catch an opponent unawares with - say ura-mawashi - to open them up for "todai"/finishing blow with gyaku-tsuki than to attempt to finish a styrong opponent with a single ushiro say.....
This is partly why I tried to focus this discussion on the "dificulty" aspects as oppose to many other aspects of technique - look forward to more topics such as "Which Kick Is Most Effective" - "Which Kick Is  Most Powerfull"  - "Which Kick Looks Prettiest" - "Which Kick is the Most Suicidal in Kumite" ÂÂ

Also good question you raised "How do you define difficult...."
Could be the Technical aspects that Azzy raised.....
Could be how difficult is it to score with.......
Could be how difficult is it to controll....
....difficult to recover from.....
