It's completely optional.

I've had this for a long time, so I don't know why it's being presented as a new option.

I do think Mozilla managed the Pocket acquisition poorly (relative to the standards I would expect Mozilla to hold itself to...other companies do far worse without being criticized, but that's irrelevant...I used Firefox when it sucked because of the greater trust I placed in Mozilla) but since then they've done a decent job, considering it's their version of the read it later features every other browser has.