All the above can be said for a Blackbear tune done with an Autocal. They are more expensive than the Diablew but IMO worth it. They've re-tuned my 02 quite a few times for no additional charge after every power upgrade/ tire size change. Plus I added a license for my 08 CC. There was a time I could roll back to stock in 5 minutes but once I installed a blower, cam, headers, etc that wasn't possible any more. Also Justin @ BB has helped me troubleshoot a couple problems via datalogging and having him take a look.
Each individual just has to decide what is important to them. If I want to play with any of the settings in my tune, takes 5 mins. If I don't like it, takes 5 mins to change back. As I understand with Blackbear, you'd have to contact them, ask for the changes/updates, they'd email a file, you'd load the tune. I'm sure they have quick turn around, but with the Diablo I have the freedom of doing it in the middle of the night, on a Sunday, etc, because it's all self contained.
For mild to heavily modified vehicles, absolutely, hands down a custom tune (from whomever) is the way to go. For a stock to mild vehicle, for me, the Diablo is the best bang for the buck.
Not to mention that if you ever sell the vehicle, all you do is roll it back to stock, and then you can sell the unmarried Diablo for probabaly 75-90% of your original cost.
Unless I misunderstand, with the Autocal, you can sell the device itself, but then the purchaser has to still buy a tune to use it. There's no way to "transfer" the tune with the Autocal even if the original vehicle has been restored to stock.
Again, not arguing that one is better than the other....just simply different. I bought my i3 as a fully warrantied factory refurbished unit, and used a 20% off eBay coupon, so it was DRASTICALLY cheaper than any other tuning option, be it HP Tuners, BlackBear, local custom shop/tuner, etc.