I've used these as well on a deployment. Each holster presents different challenges for each problem it solves.
Though I've liked the chest-rig on an IBA while in a Hummer, I had issues with the muzzle being pointed at my driver, out my door if I switched sides, or lasering my arm every time I needed to reach something. Those factors made me very leary about carrying on my chest in a fashion that allowed me to quickly get it unholstered.
I had issues with both of my thigh holsters as well. The cramped confines of the Hummer meant my leg holster was really close to the door or against the door. Trying to unholster from a seated position with a leg holster just isn't going to happen, so I improvised and installed a bracket that would allow me to mount a holster near the front of the sides of the dog-house in the hummer for myself and my driver.
It seemed that every time I solved a problem, 2-3 more issues popped up. Shoulder holsters wound up being the preferred method if we had to work in the confinement facility due to the simplicity of removing them. We found out the hard way that a shoulder holster was a very bad idea as it tends to move around on the body and IBA quite a lot.
Muzzle direction is always an issue with me and I try to maintain that discipline. To me, it's almost as important to be aware of grip direction as that can allow a BG the ability to get hold of your firearm, which is something none of us wants.