43t34fg4 Or would even a 6a to 7a/Pro be better?
Personally I think a used 6a or 7-series device, if it's in good condition at a reasonable price, may be a good way for somebody who isn't sure about GrapheneOS to give it a try without committing lots of money up front. But I would recommend that a confirmed GrapheneOS user looking to buy a new device seriously consider an 8-series device for the MTE security bump (or maybe waiting for the 9 series to come out, which might involve a price drop for the 8 series). Plus, as time goes by the USB-C external display capability will probably be more useful.
That said, everybody's situation is different, and different factors matter more to different people.