I like that they are very responsive! They have an awesome product as far back end goes so there's nothing negative about it but when talking frontend UI/UX i think their work can be improved upon greatly.
Their support staffs responses time in getting me what we need at my request has been super quick (like within minutes). If you're looking into utilizing them make sure your able to communicate well because if things go wrong or someone just doesn't understand something its hard communicating across departments sometimes especially since people speak different languages. We used IPad Checkout which was great from our customers POV however this would not let us utilize some features such as making payment without leaving IPAD checkout page only allowing purchase after user leaves app completely.