First of all, I'd be really happy to see more people escrowing Mastercoin trades. But I'm not sure if the guys at bitmit are able to do proper escrow do they even know about Mastercoin and how to determine a successful transaction?
Bitmit doesnt escrow the mastercoins, they only hold the bitcoins. Once bitcoins are in escrow, the seller sends mastercoins to the buyer. Once buyer is satisfied, releases escrow and transactions is complete.
In case of dispute, the blockchain doesnt lie. No risk to either party.
If there are any takers, please send me your offers via pm or message on bitmit.