The ease of use, it has been very easy to integrate with our own website as well! I have not found anything that i dislike about this software but what can be improved would probably just take time getting used too - so no complaints here at all :) We are using their bulk emailing service which they offer in addition if you purchase certain packages (which we did). This helps us send out newsletters regularly without having any issues or problems whatsoever from sending them through mail kithen's servers rather than ours where sometimes there could easily come errors when trying ot set up templates etc..