I've had many cars with sensors, but I've yet to have any of them fail.
I'm not too fussed either way, it has a rear camera and isn't exactly a huge car. I specifically asked Toyota UK in an email about parking sensors, as it says in the specification on the website says that they are standard, but the online brochure says they aren't (conflicting information like this annoys me so I felt the need to ask for clarification). They replied saying that they are dealer fitted option, and to speak the dealer about getting them fitted (I won't be).
My guess is that they're standard on the auto.