IMO, The Excalibrator is superior and inferior to the Predator.
The only thing I like about the predator over the current SCT package is that it can data log while the Excalibrator or 9100 Flasher can not. I have used the SCT 9100 Flasher with the Extreme Tuner Software, SCT Excalibrator with the Extreme Tuner Software and the Diablo Predator on actual cars. I would never consider the Diablo product for my own car.
The reason I think the Excalibrator is superior, is that you can change more with it than you can with the predator. Case in point, you can change the MAF with the Extreme software and tune for it, if you do that with the Predator, you must go online and download a file for that MAF. You need a PC/Laptop and Internet to do that.
Now if you like to change the settings in what you have now for mods without the use of a PC, then the Predator may be right for you. To change a tune with the Excalibrator, you need access to the software, which means you need a PC/Laptop, however you can store 3 files and the stock file on the Excalibrator. The Predator only stores one.
Depending on your definition of "Off the shelf" Tuning, then both SCT and Diablo can be considered "Off the shelf". I would say, Diablo is more an "Off the shelf" type of tuning than SCT. As I stated earlier, you can tune a different MAF in with the SCT package, you must download a file from Diablo for that MAF.
Now if your car is modded, then both SCT and Diablo are custom tunes, compared to Jet or HyperTech or whatever else is out there. The dealers for both build files for your car.
Now if I was to do it again, I would look at the SCT 9100 Flasher with the Extreme Tuner Software as my top choice. Some SCT dealer still have the 9100's available. My second choice is the Excalibrator with the Extreme Tuner Software. My final choice would be the Diablo Predator.
The reason I like the 9100 over the Excalibrator is that it can read and clear DTC codes. It also has a User Interface where the Excalibrator does not.
SCT is holding firm that the OFFICIAL release date of the Excalibrator 2, is this Monday, 15 May 2005. The Excalibrator has the data logging feature, Code reading and clearing feature and a user interface. This will be my tool of choice for my 05 Mustang.