[Coco] OS9 vs Flex

[Tony Cappellini]

As I was scanning in back issues of Hot Coco, I came across an ad for Flex.
I remember this "alternative OS" from my active coco days, I just don't
remember how capable it was.

Obviously, OS9/Nitros9 have survived over the years, so it must have had
more to offer.

What are Flex's limitations, contrasted with OS9?
Were there many applications developed for it?
Did it cost more/less than OS9?