I agree with Jordan Steele's review:
At $299, the HLD-6 isn’t the cheapest accessory on the market. You will certainly need to weigh its advantages against the larger size and cost of the grip. However, if you want a more comfortable and secure grip, longer battery life and the ability to shoot verticals in a more natural position, the HLD-6 is a very well made product, with a wonderful two piece construction that allows you to choose how you want the camera to handle. The well thought out control placement and solid build make it worth the price in my opinion.
Here in the UK, the grip was included promotionally with the OM-D. Lucky us.
I've only ever once before had a camera with a vertical grip, and it was the Nikon D2x, which was the size of the Canon 1Ds seen above. A brute to log around. And I found that using the vertical grip did not in fact improve the certainty of my grip, oddly. I don't know why, if it was because it was rounder or that the camera was much heavier. But in any case, with the Olympus grip, it's different, I do get a wonderfully certain grip vertically.
And I have never taken many vertical pictures, it's just so awkward normally. I think this grip might change it.
Just like the camera, it's a beautifully made product, it feels good in the hands and the controls feel solid.
The vertical part of it (which is separate) includes not only duplicates of both the top dials on the camera, but also two function buttons! Excellent.
Ah, one detail though: when the camera is held vertically, the information on the screen or finder does not changed, so you have to read it sideways.
Sure it adds bulk, but again, compared to conventional (D)SLR camera products, it's only about half the size and weight.
With just the horizontal part, it's still small and light:
(Credits, Jordan Steele)