Replacing Catalytic Converter - many questions

I've spent a lot of time reading... too much info... I thought I'd make a post and ask...

- What's wrong with cheapest ebay has to offer?
'Type Approved' - they're ALL type approved!!

- After fitting, should I get an MOT done!!?
Or maybe just the emissions tested??
Or is the worry many months after getting fitted?

- After fitting... what should be the FIRST step? To buy a protection kit? Best to get the fitted WITH the new cat converter??
(Or... will the thieves NOT be interested because it's a cheap replacement?)

- Protection kit - why aren't these widely available? Where should I buy from?
Why can't I find on ebay or amazon?

1 website: £99 - £350!!

Amazon, I only found this: http://www.amazon.co.uk/dp/B00HPZTCMA - not for sale anymore.

- 'It's been happening in California 10 years ago'?
This is a joke right? I thought Toyota had made a bad design and made it easy to steal.
A company like Toyota should have ENOUGH brains to work out a way to make it impossible to have stolen?
What am I missing?

- Just out of interest... what other vehicles have this problem? Is this an epidemic on many many other cars as well? Is it less of a problem for newer Toyota Prius's? Have they anti theft design or something?
I can't find protection kits for the Prius widely - but there are many for other cars.

Thanks.