I would not use them for escrow personally. An escrow should be personally aware of the terms and conditions of a trade prior to any funds being sent to the escrow address and prior to any fiat/goods/services being sent to ensure that all parties are on the same page.

As far as using coinb.in as escrow and having an escrow have one of the 3 private keys needed to send a tx for a 2/3 escrow multi-sig address (eg using their website to generate a multisig address only) then you should be able to pretty easily verify that the correct address was generated prior to sending any BTC to the escrow address that coinb.in shows.