Hey OP! I'm not an academic but a student. I've done a degree in a brick uni and now a second at the OU. Other people have outlined the structural differences which are important - and it's a great system, the feedback on work is far more detailed than I had previously.
Someone touched on student diversity. This is a major area of difference that I've noticed. As most students are "mature" they often have any combination of physical health issues, mental health issues, childcare issues, work deadlines, caring responsibilities of elderly relatives and/or children with varying degrees of disabilities, abusive relationships and unsupportive spouses - and more! Then you have the people who didn't finish school with good exam results for any number of reasons and don't quite believe they're cleaver enough to study, even while they're actually studying! Every year there will be someone studying from hospital before or after an op or having a baby!
When I was an undergrad the first time we had a "student life". Very few if any OU students have that. There's no heading off to the library with your mates to study then heading out for a beer. It's usually studying around life. And studying entirely alone. As I'm unable to attend f2f tutorials, I've not even seen another student in my whole 5 years of study. I'm not alone in that.
My first degree came from one of the red brick unis and I value both it and the experience. But my OU degree is something I am proud of (more so when I actually finish it! 😂). I also love watching the FB groups around graduation time to hear people's stories. The dedication and determination required to complete an OU degree, while fulfilling the rest of your obligations, makes OU students a breed apart in my opinion.
This is maybe - probably! - not directly relevant to your interview, but possibly provides some background info that's helpful. Good luck!