I'm coming late to this thread because I was away, but here's my tuppence worth:
The guide says clearly, right at the beginning, that it's designed to help people, not to arbitrate.
I found it helpful. I'm totally new to Orthodox worship, and while you can learn from watching the others and doing what they do, you can hardly tap them on the shoulder and say, 'ah, nice prostrations - tell me, while the choir gets going, why exactly you're doing those?' If you learn religion from the cradle, your parents and family will be much more accepting of childish questions. I found the guide helpful.
But as for cradle Orthodox finding it insulting - well, they may, but surely if you were a cradle Orthodox, you should feel secure enough in your own worship not to be worried about what a manual (which you don't need) is saying?
Also, for what it's worth, it looks to me as if being cradle Orthodox doesn't necessarily mean you can fit in with any service in any church. I noticed my partner was struggling to sing the Nicene Creed last Sunday, because it was in English and he didn't learn the English version until recently. I wouldn't say it bothered him hugely, but obviously it slightly affected his ability to participate in the service. So being cradle Orthodox doesn't give you all the answers, and if I tried to learn from him, I'd have the same problems he has with our English services.
Just my thoughts, anyway ....
I was grateful for the link, Maureen.