The UI is very simple, easy to use with good customer support when needed as well! I have been using this for about 3-4 years now but they've never let me down (or vice versa).
They are always willing/able help you out should any issues come up during your integration process or if there's something that isn't quite clear in their product documentation - which can be hard at times because of how large it gets sometimes!! Highly recommend them over other competitors like Mailchimp etc., especially since we're looking into moving from another provider who has left us high & dry after many months working together without even an apology letter / notice period given before leaving so yes definitely give these guys some consideration too. We were getting lots spam complaints due our list being used by various companies across multiple industries thus keeping people off track whilst trying make sense why emails weren’t going through properly therefore.