Whilst not being a cure by any means .... after failing to find a medication (naproxen and diclophenic) that had any effect on my pain, this ball is in real terms 100% more effective, it can stand a lot of pressure ....up to standing on it.
It goes so deep with the spiky balls, if massages perfectly when sitting on a chair for example, this basically provides a relaxtion and almost numbing of the pain in some cases, be aware it is possible to overdo it with this ball and you will feel a bit of pain the next day, as with a really good massage, however its not worse than the plantar pain itself.
Be aware this will not cure plantar faciitus in my experience .. ive tried a number of avenues, including getting the gf to massage it a lot, but for instant relief that will get you through a couple of hours .. its hard to beat !!!!