Not always. If you're building a house, you don't get it right away. Its got to be built first, but you've still got to start paying for it before its finished. Flex Pay is like that. The item isn't made yet, but you've started paying for it already. Its true you can get those items in most cases before you've fully paid for them. But Flex Pay is primarily a Pre-order tool. It allows you to pre-pay a majority of the items cost before it ships to break up the cost into smaller amounts instead of one large amount. You can use it on in-stock items though. Instead of saving up for an item and risk it selling out, you can have your order secured and 'save up' buy paying the monthly payment. That way you can still save up, but still secure your order.
Flex Pay is meant to break up the cost of large purchases. For example, the recent HT Batmobile. $630 is a LOT to spend at once. But if you use the Flex Pay offered, you can pay as little as $53 a month for 10 months. That isn't nearly as bad, and can be easily squeezed into a collecting budget. $630 is a lot harder, even if you are saving up on your own for that one-time payment.
Flex Pay works for some and just doesn't work for others.
If its not your thing, accept it and move on. For others, its a life saver on high dollar items. Its there as an option, but not something Sideshow is forcing people to use.