2005 VW Polo 1.2 - Lambda Sensors - PX-230A

I'm having a new cat fitted this week and I've been advised to fit new lambda sensors too.

Just looking online at prices - is the pre cat sensor exactly the same part as the post cat sensor? The ones I've looked at for my car don't seem to specify whether they are pre or post. Can I just order two sensors and they'll work fine?

Thanks.

2005 VW Polo 1.2 - Lambda Sensors - elekie&a/c doctor

Why do you need a new cat,and why does it need new sensors.?On this car the front and rear sensors are different.