Binance is Prime's biggest customer if you're talking dollar volumes. Also, when Scott Purcell left Prime 2 years ago, he says the company was profitable and properly diversified.

He made the statement on his LinkedIn about Fortress Trust, of which Albert Forkner (former Wyoming State banking commissioner) is the CEO:

Prime Trust is a trust company, so if they fail to hold Swan's clients' BTC in customer name (which would allow customers to withdraw to their wallets/move to new custodian) then they're all going jail (and PT is going into receivership).