Not sure if you purchase one yet, but I've been using the Hakuba KGP-02 for approx 5 years without issue and I love it. Originally had it on my XT, then moved it to my 20D and now it's on my 40D. I just haven't been able to find a comfortable neck strap and I don't particularly care for my camera dangling in front of me, so the grip was a natural choice. During my kids sports, I tuck the camera to my body like a football and I can run up and down the sidelines without issue. When walking in crowds I usually tuck it into my body to avoid collisions and when hunting for wildlife I relax my arm and allow it to naturally sway back and forth while I walk... I don't even have to hold the camera tightly... I just relax my fingers around the body and allow the grip to handle the weight. I won't lie, once I switched to the 20D and the 100-400 IS the camera felt a little heavy, but I eventually got used to it. I can't remember how long it took, but if I recall it took a few weeks.
If I need to use a mono or tripod I use the foot of my 100-400 IS, so I have never tested how well the threaded screw works; however it's only a few twists to unscrew it so I don't see it as being an issue.
The only downside to the grip is that the mount covers the battery door. After years of use I can honestly say it's not a big deal. Quick turn of the screw to loosen it a little and I turn the mount slightly to clear the door. Battery changes have never bothered me.
When I purchased my 40D I gave the 20D to the wife and to my amazement she immediately asked me if she could keep the grip as well. I chuckled but couldn't part with it so we had to go to the local store to get another one.
Now it just feels like an extension of my hand... extremely recommended...
I can take some pictures if you wish to see how it covers the battery door, but here's all I could find...
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