I've done a few OF subscriptions, the girls are almost always offering deep discounts, e.g., $3/mo.
From what I've seen, you're about as well off just following them on Twitter, you're getting the same nudes and short clips. Almost no b/g content.
I let the subscription run out after a month for all three.
What I would LOVE is if some AMP providers had an OF, I'd subscribe for sure. Asked a couple of the OF girls if they provided on the side and all got really offended lol.