You dont need one, however it might be helpful as with the location of the lambda sensor, the wire can become quite tight.
When I fitted mine, I just pulled a bit more cable down, its tight, but got enough slack to not break the cable.

 

Mine
I never fitted one.
How do you free up a bit more loom?

 

You have to get under the car, see where the loom travels to and from, I cant remember exactly as it was a while ago that I did mine, but i think the cable passes through some cable tie clips or something, you wont be able to move it a whole lot, but it will be enough.

 

I unplugged mine as it wouldn’t come out of the cat anyway and after screwing it into the cat plugged it back in and there was plenty of slack 👍

 

In reality the 90 degree elbow is not so much to provide for any extra cable it is more to negate the chance of your EML coming on. With a decat it is an almost certain need. With a sports cat you should be fine without it.