I use a similar strap on my camera. My camera has a built in "battery grip". The strap attaches to the top and bottom sides of the camera.
I love it. I use it far more often than I do the neck strap.
1. what do you do if you stop for a quick drink or let's say a hotdog, at a ballgame or something, I can let mine hang around my neck briefly...?
When I'm going to be out for a long day (like a typical WDW day), I use both. The neck strap attaches to the top of the hand strap and to the other side of the camera, so you can use both at the same time.
2. doesn't your hand get tired after a whole day of carrying it ?
When adjusted so that it fits snuggly, your hand doesn't have to grip it with much force at all. To me, that's one of the key benefits of the hand strap. It keeps my camera in hand with almost no extra effort.
Even though my hand is usually OK, my arm gets tired if I spend enough time with it. In those cases, I sometimes revert to the neck strap or I carry it in my other hand (just grabbing the strap with my fingers).
3. do any of you have your flash mounted on it while carrying that way, I don't know that I'd like the extra stress on the flash mount. ?
I do that all the time and have not seen any ill effects on either my flash or hot shoe. Of course, I'm known to be a little reckless.
4. anyone use a lens such as an 80-200 2.8 I know it's debatable, but I sometimes carry mine mounted for hours, I feel safe with the lens cradle that I'm avoiding mount damage.., as opposed to supporting this setup by the camera, rather than by the lens as recommended..?
Again, I do this all the time. I've been doing it with the same lens and camera for about three years and have seen no adverse impact. Of course, that doesn't prove anything and certainly doesn't imply that it is safe for all cameras and all f/2.8 telephoto zooms. I'm just presenting my experience.
5. if carrying all day, wouldn't that increase the risk of banging it against something, I guess my concern is that if I'm out somewhere shoting al day, my flash is on my camera...?
I find it safer than having it dangle on my neck strap. Still, it is a constant concern, especially when walking near kids. In crowds, I often lift it up and carry it on my shoulder. I'm always terrified that I'm going smack a 3 year old in the face with 6 pounds of metal and glass.
7. do any of you have a vertical grip, it seems it would be a minor hastle sqitching to vertical if using a vertical grip.
As stated above, my camera essentially has a built in vertical grip. With my prior camera (Canon 10D), I almost always carried it with the vertical grip on it. In fact, the hand strap that I use would only attach to it with the vertical grip in place. I guess my suggestion would be to either buy two hand straps (one designed for use with the vertical grip and one designed for use without) or buy one for the configuration you most prefer. I don't know of any hand straps that work both ways.
I have to say that the one drawback I've found with the hand strap is that it makes portrait shooting a little more awkward. I am tempted to keep my hand in the strap, but I don't find that nearly as comfortable for shooting portrait shots as having my hand on the portrait grip.
If you aren't particularly interested in a hand strap but are looking for something better than the strap that came with your camera, there are other options as well. I would strongly recommend a good neck strap (the OpTech's seem to be quite popular). You might also talk to WillCAD. I seem to recall him posting something about a new harness he was developing.
You can even switch to holding the cam in your left hand to give your right a break.
