I've had my Fly-Jumper's for a good few months and not had to replace anything yet. These arn't "pro-jumps" from here so wether this topic is sensitive to the manufacture of PJ's I dont know.
My mates have had to replace their rubber feet but thats after 3 years , works out as 2 years hard work.
You need to keep in mind that these are prone to wear + tear so cant really help it.
What parts have you heard need replacing?