The catalyst problem was identified and fixed by TTE some time ago. They issued a revised sub-ecu (alloy cased - superceded one is black) with 50rpm lower rev limit which stops the fuel cut off occuring and hence the damage to the cats ...
Unfortunately, LGB have early revision s/c kits....
I can fully understand LGB wanting to make absolutely sure the kit is right before releasing it to the public - they've built a brand image around quality and reliability which they want to keep.
While the likes of us might not worry about the odd little problem cropping up given the bonus of an s/c kit, other owners may be less easy going which could ultimately damage the Lexus brand image.
However, i do find the disinformation you get from some dealers rather disappointing - you know the kind of thing .... What do you know about the TTE s/c ? Ooh no sir, you don't want one of those - it'll blow your engine up for sure - happens all the time ....