Is the Filler up club scam?

It's a scam. When you pay your money to them upfront, you will be introduced to Multi-Level Marketing. There is nothing I can tell you about MLM that you can't find out yourself by googling "Pyramid Scheme".

You will not be paying 1/2 price for gas as claimed. You will be alienating family and friends by trying to trick them into this foolish scam. Even assuming you succeed at tricking them, it still won't work.

And guess what? Your credit card is still being charged. Membership fees, add ons, upsells, extras, etc. A pity you aren't saving fifty percent on gas, it would have come in handy to help pay all the extras they sock you with.