I have this grip for my OM-5 camera. The grip does what it is designed to do very well: enhance the camera's ergonomics when a large lens is attached. For example, without the grip, the 12-100 f/4 lens on the OM-5 body is not comfortable to hold. With the grip, it becomes much more natural to hold the camera, even though the weight of the grip is added. The form and contour of the grip very much resemble the grip on the E-M1-mark III (and mark II) cameras. When measured, the OM-5 with the grip is about the same depth as them, with maybe a few millimeters difference (I measured the OM-5 with the grip to have a depth of 71~72 millimeters, while the E-M1 mark III's official spec is 68.9, so 1~2 millimeters difference. In practice, they are effectively the same). I tried holding an OM-1 in hand in a camera store (OM-1 being very similar to the E-M1 mark iii), and alternated between it and my OM-5 with the grip several times. They both feel more or less the same in hand. Well, maybe not the "exact" same feeling, but 90% similar, to me anyway. It weighs 120 grams. The OM-5 weighs 414 grams, and together they weigh 534 grams. An E-M1 mark II weighs 574 grams, so the two bodies would be less than 8% different in weight. It adds exactly 12.5 millimeters to the height of OM-5, making the combo about 7 millimeters taller than the E-M1 mark ii/iii. This is a good thing, since my pinky finger can end up on the grip area (as compared to under the camera) and help holding it. It MIGHT have been nice to be able to assign different functions to the camera's front dial and shutter release once the grip is added. BUT, ergonomically, once the grip is attached, pressing the camera's own shutter button needs too much finger twisting anyway, so for me that's not a factor. The position of the rotating dial around the shutter release button matches the design of the E-M1 Mark ii and iii. The feeling of the rotating dial on the grip slightly differs from the feeling of the dials on the OM-5. While it is metal and it clicks as it rotates, it's a little more resistant to rotate, and the clicking sound is a bit more muffled. It is not a dealbreaker, but it would have been nice to match. The grip is well made and doesn't bend under pressure. It would have been nice if it had an opening to change the camera's battery without needing to remove the grip, but I suspect such an opening may have affected the structural stiffness of the grip, since the OM-5's battery door is pretty large. Yes, it is an inconvenience, but to me it is not too big of a deal. The grip has a little storage space to hold the connecting pin's plastic cover. This cover seems to be necessary for the OM-5's weather resistance, so it would be bad to lose it. It's a nice touch to have that storage in the grip itself. The grip itself is supposedly rated to be weather proof. I was at first worried about the exposed pins that connect the camera to the grip, but the pins on the grip are raised, and at the base of the raised platform there is a flexible elastic ring that gets snug against the base of the camera once the grip is secured. This makes me believe the combination of the grip and the camera are probably as weather-sealed as the OM-5 itself. Again, a nice design. To me, with the grip attached, ergonomically, the OM-5 becomes equivalent to an E-M1 mark II (seeing that both lack a joystick and almost the same number of buttons on both bodies), both in terms of dimensions and weight. This is a great thing! Whenever I need to use a longer or heavier lens, the OM-5 transforms itself into a pro-series body ergonomically. (Note that internally, the OM-5 has the very same Truepic IX processor and the same sensor as the E-M1 mark III, so the picture quality is the same, and the very same performance for autofucs and computational features, etc.) But, with a lighter lens, the grip comes off and the OM-5 becomes light and nimble again. Without the grip, I tend to limit the OM-5 with lenses lighter than 400 grams or so, and anything heavier than 500 grams would definitely benefit from having this grip on.

I have mixed feelings. On the plus side it really is far more comfortable to hold the camera with this grip in place and the placement of the grip's shutter button is much more natural. The grip itself is made of high quality materials and the dial is very satisfying to use. My main complaint is that it does not add any functionality to the camera by having another dial and button. The shutter button and dial on the grip is redundant to the existing shutter button and dial. You cannot assign a unique function to each one. I had hoped to use the grip's shutter dial to control aperture, the old shutter dial to control shutter speed and the rear dial to control iso. This cannot be done. Whatever you set the old shutter button/dial to is cloned over to the grip's shutter button and dial. If they functioned individually from one another this grip would have been well worth the money. Now it's more or less just there to improve the ergonomics of the camera. I doubt anyone will write a firmware update for this grip to add this functionality now. It's still a nice grip however. If you're after better ergonomics it certainly accomplishes that. It also looks quite good on the camera if that sort of thing is important to you.

Why would Olympus offer an accessory Grip for the OM-D E-M5 MkIII that cannot access the battery compartment without having to remove the grip each time? Great camera.., not so great accessory. It's a deal breaker for me.

This is a huge step back from the HLD-8G. There's no way to add a true battery grip beneath it, and there's no headphone jack. I would strongly encourage Olympus to replace this with a more useful accessory grip more like the HLD-8G.