are we talking about MBTs here?
I have plantar fasciitis too and wore MBTs exclusively for about a year. They did help the PF to calm down a lot, I can't say they helped with toning though. What did happen though was that I got an absolutely horrible ankle sprain wearing them - they have very little stability on the side of the shoe and when I was walking out of the door one day I turned to lock it, the side of the left shoe collapsed against the edge of the doormat outside, and I swear my ankle tendons nearly broke. It was agony I tell you, but more than that, it's been nearly a year now, and I can not regain the stability in that ankle
PT, stability training and splints all aren't helping, and I can't walk or jog outside or on uneven ground without support any more.. all because of a stupid shoe.
I've read plenty of other people have had similar injuries because of the MBTs as well. So, definitely not worth it in my opinion!