The Plantar Fasciitis condition builds up over a long period of time, and similarly it's treatment takes a long time too. The use of these heel pads assists with that process, so I'd recommend you use them in all your shoes, both now, and in the future. The thickness of the product is irrelevant, the materials and design are what makes these heel pads market leaders.
I had the same problem about 6 years ago, and began using these pads on the doctor's advice. It took months to settle down but happily, I can tell you I haven't suffered for probably 5 years now, and yes, I do still use the shoes I wear to work all day.
Hope this helps.