Tom-
The SCT X3 before it installs the new "tune" it loads the one already on the ECU to it. So if for any reason it can easily be returned to its original profile. The SCT is an option with the
Bostig Zetec conversion. The user doesn't actually use the device to change settings but uses it to load the software after it has been downloaded onto the SCT. It's also has the
ability to live monitor and data log the run. The data log able to be uploaded to a PC where it can be viewed of emailed to Bostig for review. As with most reflashers it has the ability to
check engine codes,reset codes,and turn off the check engine light. 
I have one that I got with my NA Zetec conversion and I still use it with the Beta turbo install to reflashers the ECU. I now data log/moniter with a Dash Daq. 

Bill
87 Westy