it's a six !!!!
That's not my experience here's a Bosch wiper blade that's at least 3 years old on my car. Here's the passenger side Michelin wiper blade that's been on for 6 months. I've never had rusty wiper blades before....
Same happened to me and now using Valeo with better results.
It's not about that. I'm conscious about reducing my carbon footprint and don't want to order stuff if it's just going to sit in the shed (annoyed)
There are different fitting types too and some rear blades have a proprietary fitting. These won't be good blades but probably OK on the rear for a while IF they fit. Cheap but potential wasted journey to collect if not.