Matrix, unlock one phone and update via SUS. Of course, everytime that you flash and update with cruiser it will patch again the GDFS, then use the SonyEricsson free service (as our clients will do too).
When you reflash the cellphone with Cruiser, do you write GDFS? No, and if you do it, it will ask you to use one log (to generate the patched gdfs)
Then you will have the answer to your question. If the phone become's locked again, you'll know how real is the "permanent unlock".
The difference between bouth methods is... that there's not difference. It's a copy/paste, and Cruiser lies about some characteristics of the method, to make it look "a little better".