I also have GDE, like Ram For Life said, one of the reasons I went to GDE was reputation and years on the market. GDE has been around quite a long time, and when I did my homework on the different tunes, I have a difficult time finding any complaints about GDE. I got it for a few reasons.
i) REGENS was a concern to me, as my truck (stock) was going into regen every 150-250 km. This uses up more fuel lowering fuel economy, and unburned excess fuel from a regen could have the potential of contaminating the oil. I looked at is as every 10,000 km I changed my oil so the oil had about around 60-68 regens happen during it's life-span, which increases the possiblity of fuel dilution. With an already troubled motor prone to lower end bearing failure, I didn't need to give the truck any more reasons to blow a motor. NOW - with GDE, my regens occur every 1200 km give or take, so that's 9 regens / oil change which is a dramatic difference.
ii) I wanted to turn OFF the soot making EGR which was contaminating my intakes, plugging my MAP, and choking my swirl valves. At the time, my truck was still fairly young, 55,000 km, and the soot wasn't crazy like some have posted, but it was definitely accumulating and I didn't want the problem to get worse over time.
iii) I hated the stock lag when you jump on the highway and the truck didn't move!! GDE gets rid fo that.
iv) MPG has definitely improved, not only on highway, but city also! In the city, with stock, I was averaging around 10-10.5 L/100 km, with GDE I average between 8.5-9 L/100 km.
v) I like to buy things based on many many positive reviews and with GDE being around for so long, there were lots of happy customers. I also do google searches for GDE COMPLAINTS, GDE problems, etc to see what comes up. People will always complain when unhappy.
vi) In ontario, they just scrapped the emission testing so I"m good until the next government gets voted in (4 years...)
Do your homework, find out what works best for you, depends where you live, what the epa rules are, do you have emission testing, what do they look at, ask lots of questions, pm guys that have different tunes, some will tell you the good and the bad, etc?