It has a horrible negative side, whereby if you don't get something it's because you didn't manifest it hard enough, so it's all about victim blaming - there's no acceptance of things like bad luck, privilege, etc.
I have a friend who is heavily into it, but she's enormously privileged, was also incredibly lucky and then with all that abundance has now decided she 'manifested' it. She knows something more than hard work contributed to her success (she works in an intellectual field and isn't that bright, which she used to acknowledge prior to getting into manifesting). The friendship is somewhat strained at the moment because rather than accepting the role luck played in her success (which would have involved a little humility and honesty), she has decided it was wholly down to her 'manifesting' it, which somehow makes her better than the rest of us who are just not wishing hard enough. Her ego has been allowed free rein (in manifesting terms, she has removed all 'blockages'/obstacles), and honestly she's insufferable.
It is like cult thinking, because she has to block out the realities of life - luck, good health, chance, being in the right (or wrong) place at the right time, being white, slim, blonde, coming from a wealthy background, having a supportive partner. None of these factor in her understanding of how she's come to be where she is.
The worst is that her response to anyone having a tough time is to send them articles on manifesting, which is rather like sending articles on personal safety to someone who has just been raped. Not helpful, not compassionate.