They don't exactly require Plaid, they can also use a debit card or ACH. You have to email support for the privilege though.

I had tried Plaid at first, but quickly switched when I found out that they would watch your bank balance and disable your Privacy account if it went below $50. They would require you to prove a balance of at least $50 in order to enable the account again. Fortunately, both of the other methods don't really care, and as long as you disconnect Plaid while your balance happens to be over $50, your account will stay enabled.