How effective is it to do daily stretching for the legs in order to get a better foot technique for kicking, like in Karate or Taekwondo. Let's say, I am stretching my legs three times a day for about 5 minutes. Will this help me to improve my foot technique or is it even harmful for the tendons and muscles to do so? I'd love to hear some experiences people made.
I would say there is a difference between good technique and properly performing high kicks.
You can develop good technique practicing with lower kicks. For example, a side kick involves specific movements, from chambering to the final leg extension. These technical movement can be trained at the height your comfortable with. That could be at knee height.
Stretching will not improve your technique. It will improve performing these techniques as high kicks.
Stretching alone is not enough enough for good high kicks.
You need the proper muscles to be developed, and much of that happens while working on the technique.
So you need both if you want to develop good high kicks.
Will stretching be harmful?
No if you don't overdo it.
Don't over value it, you don't have to do the splits for good high kicks.
It reduces resistance slowing down the movement, but technique and all the necessary tiny muscles are more important in my experience.