Theoricaly, the good practice for hide the toc html page, it's to set the attribue
linear to
no at this <itemref> in the <spine> of the OPF... however all e-reader do not seem to respect this element and still display the page, so your solution it's not so bad (as long as you put the toc page at the end of the book)
A more radical solution would be to use a ePub2.
Code:
<spine>
...
<itemref idref="toc.xhtml" linear="no"/>
</spine>