What is the difference between Felt credits and subscriptions?

Subscriptions are a monthly membership that rewards you with a huge discount if you use any of your 3 free subscription cards that month.  That’s right!  Each month, you receive 3 free cards with up to 4 frames each (a value of up to $18.00)!  CAVEAT!  The subscription cards don’t roll over each month; if you don’t use them, you lose them.  Credits, on the other hand, are a simple way to receive a discount when ordering a large number of cards, and they never expire.