ok guys have spoken to magic and i will explain the problem for the bolt on cats.
The hole that you screw the temp sensor into is not a problem, it is just a normla threaded hole.
The problem is that inside the hole there is a fitting that holds the sensor. This is the problem, Magic say that without it, the sensor itself will move around in the cat and it will not work properly.
I am not sure if other aftermarket cats come with the fitting, or just a hole in the cat, they will be looking at d00ds car tomorrow, and i might have a look at mine a a bit later to see if my compliance cat has the fitting to hold the sensor straight.
They are waiting to hear from a supplier of theirs if they can get these fittings, if they cannot, the only was to have the sensor fitted properly is to send out your old fitting.
The compliance cat they were sent already had the whole lot removed (im assuming it was removed to be welded into another cat)