I found you reverse much better after hitting a few things. Try a toe bar, saved me on a few occasions over the years *laughs*
I have a Fiat 500x with all the gadgets, don't like it as it makes me nervous beeping when I am miles from anything. Had a rear camera on a hire car and that was even worse. I shut my eyes and go back until it feels right (the force is with me)
I would say sensors are not necessary in a 200 - it's a small and easy car to manoeuvre in reverse.
I've had a few cars with sensors and the only one where I found them useful was a Ford S Max due to its awkward shape. Even then it was the front sensors that were more useful than the rears.
If you're fitting an aftermarket kit, why no go for one that uses sensors which mount inside the bumper rather than through a hole? Preserve the look of the car, no drilling, etc...
The sensors on the 25/45/75/ZR/ZS/ZT/MGF/TF are a reminant from BMW, well worth raiding
the scrappy for a kit, its just the 4 sensors, a box, sounder and its wired to the reversing lights.