I had a DiabloSport predator on my 08 hemi Dodge Charger - lots of positives, but a couple of negatives that made me end up taking it off.
1. Yes, it did make a noticeable difference in acceleration on 93 Octane.
2. Made the throttle feel more like a cable, so it was a steady acceleration.
3. Allowed me to adjust the transmission to shift more quickly.
Overall I was happy with it for about 3 months, then I noticed the transmission started making a strange noise when decelerating from 2nd gear to first. I had the autostick option and it DIDN'T do it when I would shift manually between 2nd and first. Ever blow over a bottle and it makes a sound? Kind of like that in rapid succession, followed by a vibration. Did this consistently every time. Since it was new and under warranty I decided to remove the tune and take it to the dealer to have them check it out. First time I drove it after removing the tune the sound and vibration was gone and it drove normally. Put the tune back on and the vibration and sound was back with it. Removed it and never put it back, and never had a day of trouble with the Charger after that.
I also had a DiabloSport Predator on the Corvette (2005 Z51) for a couple months and I just removed the tune from that car last week for two different reasons - 1, it was TOO powerful for the stock tires. If I put it to the floor from a dead stop it would spin the wheels like my 68. If I was already traveling around 30-40 and hit it, it got really squirrely. A stickier tire may have solved that, but I wasn't about to throw out $1700 worth of Goodyear F1's away. The other issue was that I started getting a "Service Charging System". Every 3rd or 4th start it would come on while the tune was installed, and never came on since it's been removed. Dealer inspected the charging system and both the battery and alternator are fine.
So while I can't speak for what it would do to a non-performance vehicle, those have been my experiences on two different vehicles with Predators. The performance was certainly there, but for me the side effects outweighed the benefit of the extra power.