It's the same as saving your money by setting it aside...
There's absolutely zero benefits by flex paying, except SSC getting an interest free loan, that's it.
If you flex, and you find yourself with money trouble, SSC will take a cut from the refund they'll give you.
If you save your money (you CAN do it) and life gives you trouble, guess what? You can use all of that money towards whatever that is.
I never understood the mentality towards flexing. It's not a "favor" by SSC. It's a genius way of getting interest free loans from customers and then getting even more back because a lot of people cancel because they realize they can't afford that many dolls. You are not saving a dime. You are not paying less. It's your brain making you believe that.
Save the money, pay in full when the item comes out. Nothing sells out anymore. But If you MUST preorder, use BBTS.