Clicking yes/no in a little menu (Diablo canned tune) vs making your own adjustmens (Hptuners) is comparing Apple vs Oranges, and in this case, Hptuners is a lot more flexible, and will allow you to dial things out regardless of mods. There is really no comparison, lets put this way for easy reading, one is kiddy toy, the other a man tool, honestly. Even if you're going email tune route, Hptuners will allow you to see the changes in the tune, assuming your tuner doesn't tuner lock the calibration (some do, it's up to you to find ahead of time if your tuner is one of those)
the biggest con of Hptuners is the time it takes for you to understand what needs to change and why, there is a lot to read, lot to digest, and a lot to learn, learning requires self investigation and also help from the tuning community, which is one of the biggest assest for HPtuners.
If you thought you wanted a simple way to say you're tuned, you're not going to find that in the Hptuner user interface, Hptuners is a pro tuning suite, so it's assumed you know what you're doing, if you want the equivalent to that in Diablo, you need to buy Diablo CMR, which is also not a yes/no handheld thingy. So there is niche for each application. if you wanted to slap a CAI and say you're tuned, then perhaps the handheld might suite your needs.
Hope it helps.