It's worth reiterating that this viewfinder is external and does not talk to, or get any messages from the camera. Therefore you won't get any information whatsoever about your metered exposure, or more importantly what the camera has focused on. But the VF-1 is still in my opinion worth having, because it enables you to compose your image well, even if you use a Panasonic 20mm f1.7 lens. I understand that the field of view offered with the latter is more accurate than the cropped reading given by the viewfinder when Olympus's own (inferior) 17mm f2.8 pancake lens is attached. Also, I am firmly of the old-fashioned view that a viewfinder helps considerably to stabilise the camera, and having it as close to the eye as possible feels like a much more natural position for the camera to be.
I recently also purchased a medium sized, retro styled carrying bag for my E-P1 camera and unfortunately the addition of the VF-1 causes space issues when it's attached in transit. However, it's very simple to take the accessory on and off and therefore like practically everything else, there's a way around the problem.
For a relatively experienced photographer, the lack of a viewfinder seriously detracts from the basic Olympus E-P1 camera. If like me you're accustomed to having one at your disposal, you will certainly regret the omission. This one is by no means perfect, but it's much better than nothing.