There has been multiple threads on this.
I have the GDE tune on '07 JK. It has a hi flow 200 cell catalytic converter with a small straight through muffler. From the back of the turbo to the exhaust tip there are no restrictions or bends that are not mandrel bends, The exhaust was restricted behind the turbo so the exhaust shop opened this up to the same diameter as the exhaust. A pyrometer was also fitted.
The previous owner tested the GDE tunes on the dyno after exhaust mods were complete. The max EGT limit was 500deg. 9 runs altogether were undertaken to get a good average: 3x Runs in STD, 3x Runs in ECO, 3x Runs in HOT.
Dyno sheet is below, but results were as follows:
HOT (red on graph) 114.8KW / 490NM
ECO (green on graph) 113.4KW / 480NM
STD (pink on graph) 89.4KW / 370NM
From the dyno results it was concluded that the hot and eco tunes are almost the same except for one big difference, the exhaust temp in HOT is up to 500deg C and rises very quickly when accelerating, so it's pouring in more fuel for just 1.4KW power increase which doesn't seem like it was worth stressing the motor for
Post the dyno test, the previous owner ran it in ECO obviously and I am still running in it ECO. I haven't had any engine lights thrown.
The other usual question is if it's worth it? Outside of the performance and apparent economy improvements (I've only ever know the economy based on the GDE tune, so I don't really have anything to compare it too. Other can probably weigh in?), I think it is purely worth it for engine health avoiding most of the exhaust gas recirculation