The fact that you want the service to be a cash transaction. When a thing isn't anyone else's business but yours, you might not want a paper trail with identity involved.
I guess you could search for other carriers of the service that would accept money order payment. At least that way, you're handing cash to a live teller without ID.
I never heard of any service with fees deducted from your paycheck or benefits.
They might have direct debit from your checking account if you'd rather not use credit cards or debit cards.