Re: Kotegaeshi, help please
It's probably best not to practice technique outside the dojo on friends, unless they are receptive and you are fairly advanced. They may not be prepared, might not know when to slap out, may not know how to get out of a hold or lock, and aren't dressed for taking falls or on a soft surfaced floor. If you do want to show friends, I suggest just showing them the power but not doing it hard. You can hurt someone!
As far as for effectiveness, you're losing the element of timing since they never attacked you I'm assuming. If I was going to show an outsider something, I'd probably show them the Sankyo position and let them tighten it up if they want to.