I'd suggest if you already have a PC, keep it.
I mean...how much can you really get for a used PC?? Plus the PC is more versatile...more backing plates and utilities like carpet bushes and such. And as you mentioned it still can be a backup.
DJ Jonny and I discussed this and we both agreed that we still needed/used our PCs. Beside the carpet brushes and such, the PC is better suited for applications of products like
AIOs/Glazes/Waxes and such. The
Flex can certainly be used AIOs/Glazes and Waxes...but it can be a little overkill. Plus being able to palm the PC and literally feather it around is a bonus for non-polishing applications.