No, I wouldn't. I know my mum tried to get an older seat (maybe 5 years old) installed and the installer wouldn't do it b/c it didn't comply with Australian Safety Standards.

I'd be concerned about that, given that convertible boosters are now made which suit 8kg-26kg, so essentially 6years.

Thanks for all the replies. We don't really need that seat in DH's car, it was more of a 'just in case' but the chances of us needing it would be slim to none.

DS's seat will be going to bub, and DS will be getting a convertible booster