the tunes that come on the device are "canned tunes" meaning that they are the same for ever car, a dyno tune means that they put YOUR car on a dyno and then tune it, there could be slight difference or issues that a dyno tune will show that a canned tune will not. also you can usually squeeze a little more out of a dyno tune because they can see exactly what your car is doing and make adjustments from there, with a canned tune it has to be good enough to work on any car right out of the box.
however, because of the price of a dyno tune, it may be a little more than what a completely stock ls needs, that being said, ordering the tune from a person that actually works on this car (like torrie for example) is even better than the tunes that come from the manufacture as he has a better understanding of what these car like and how it responds to different adjustments and can customize the tune to what you want.
long story short, buy the device from someone like torrie instead of a website just selling the devices, the preloaded tunes are better than nothing but a good tuner can maximize it for your application, even if stock.
also i have no idea if anybody does tunes for V6's