Yes, it is absolutely safe to pay via the platform. Payments are not transferred via the Eyevestor BV but are transferred via Stichting Derdengelden Eyevestor. This is a company which transfers the money (minus transaction costs) directly to the eyeventure, Eyevestor has no active role in this process.
The moment the payment is completed the position of the buyer and seller will be adjusted. In the meantime the eyecons will be 'in depot' and is trading with those eyecons not possible.
In the case of a dispute between buyer and seller over the payment, will Eyevestor be the middle man and will help to solve the issue.