It's a question that sometimes arises, I believe among kendo-ka outside of Japan.
The short answer is that a shinai is very different in almost all respects to a katana; so it's just not the handle (tsuka).
But the interesting thing, when I do Iaido and pick-up my iai-to or kendo when I use my shinai it never enters my mind that I'm dealing with something different. Of course, in Kendo we treat the shinai in the same manner as a Japanese sword, respect, comportment, etc.
As to insuring that the tsuru (string) is up and correct for a valid strike, make sure tsuru is facing down in sageto or taito so when you do nuketo and take chudan no kamae the tsuru will always face up correctly.
Officiating seminars teach us to make sure the tsuru is facing up when a strike is attempted so officials are quite proficient in detecting this. But in my mind, shinai and sword are one.
Kendo-Guide.Com: Thank you for your comment. I started iai under the instruction of Alex Bennett in New Zealand. Of course, there are some different between iaido and kendo. However, as long as we do the right things in kendo, it is not that hard to learn iaido.
I really recommend that kendoists do iaido if they have an opportunity. It makes us understand both kendo and iaido better.
