For the past 11 moths it has been worth while. However Amazon have now implemented an opt-out feature for buyers. Meaning those who opt-out do not received the emails sent via Feedback Express. Currently 1/3rd of my messages aren't getting through to my buyers and i'm concerned this will only increase as people become aware of the opt-out feature in the coming 12 months. So basically i'm not getting the serviced i paid for (Amazons fault not feedback express admittedly). Therefore i will not be renewing with feedback express.
UPDATE:They have now alleviated my concerns UPADTE: They promised me a 33% recurring discount, only a few months down the line, they have now withdrew the discount. Avoid - not worth the hassle.