Tekki is a Shotokan version of Naihanchi. I do Shotokan myself and have been training Tekki Shodan quite a lot this spring. However, I haven't done any bunkai for it, just the movements. I know that there is a lot of nasty bunkai for Tekki katas, some people consider them an "application goldmine". In Shotokan you stand in a wide kibadachi stance during the kata. The stance should be strong and stable and shouldn't collapse at any point. If I compare Shotokan Tekki to the one those Okinawan Senseis in the video are doing, I think that the major difference comes from the kibadachi stance. Those Okinawan guys use their hips very strongly. Shotokan kibadachi is much wider and because of this, you cannot use your hips much. In fact, if you use twist your hips in Shotokan Tekki, you are doing it wrong. The hand movements in Naihanchi Shodan and Tekki Shodan are quite similar.