I did *not* use any isolation transformers. And as far as I can tell, there has been no ill effects. I also saw on other threads, where others did not include the transformers and seemed to be operational.
However, with that said, if you have everything together, why not keep them? I really don't know enough technically on this point to provide any guidance. I remember my 8th grade math teacher beating into my head that just because you found one example of where a proof was correct, that doesn't mean it is a proof. :-)