Review on Opt-Inbox by Jake Atonyo

I like how it works with Google apps such as Gmail, so if somebody is signed in to their gmail they can still optin for our newsletter without having an extra step of signing up through us first! And also being able not just be sent emails but actually text messages too which i think makes sense since we do have customers who might prefer this over emailing them or calling etc., especially when its about something urgent/important enough where people would rather take time out instead doing other things online (like playing Candy Crush). But at same times sometimes there are issues sending texts via InBox app because even though my phone says SMS delivered successfully yet nothing shows inside GMAIL inboxes after 24 hours later?