Stumpy,
I have used them in a couple of tanks and even in battle at The Danville Museum's indoor battlefield. They do give you the ability to adjust the speed so that the tank ramps up to speed without jerking from a standstill and you can adjust the inertia so that the tanks coast to a stop just as a real 30-60 ton tank really would.
However in a battle both these are negatives, as some of the comments mentioned.
Mainly the problems are when you see someone firing on your tank from across the battlefield by the time you throw the stick to move you out of the line of fire, before the tank starts moving you have been hit. With the inertia set properly you will definitely run into obstacles, as it is very hard to let up on the throttle at the right time to roll to a stop before contacting a building, or rock or another tank.
When I set mine up for battles I would cancel the inertia for the battles so at least I could stop quickly, I didn't want to risk running into the river that runs through the scenery, it also made it easier to move the tank into a firing position and stop where I wanted it to be. Before I adjusted the settings when I would try to take a position on the reverse slope of a hill I had a tendency of the tank coasting over the top of the hill and putting me into the line of fire.
So for just plain driving the tank in a relatively open environment the Turnigy works great it simulates the movement of a tank pretty accurately, in a battle you will want to disable or minimize it effects as it will put you at a definite disadvantage with it enabled.
Steve