That's true.... for the E-300/E-500/E-1, that would be the only alternative
I do believe that the E-330 is not designed to take a vertical grip. A vertical grip is not in the list of supported accessories in the info sheet that came with the camera.
But do you really, really need the vertical grip in the first place?
When I had the E-300, I always took it off when I travelled as it made the camera very heavy, bulky and uncomfortable to hang around my neck the whole day. That was why I did not care too much that the E-330 did not have a vertical grip.