I really like that you can get notifications for when an account has been created or deleted from your list automatically without having to poll it every day! This makes my life soooo easy as now i don't have worry about forgetting if someone exists/has existed at their old mail box layer addresses anymore :) It's super cheap too -- which was also great because we were able use this with our small team (about 5 people).
So far no complaints - but then again its still very new!! We're only using them currently through Zapier integration into Slack channels where they are used during onboarding conversations etc., however there may be other ways around doing things here such as sending emails out directly after creating accounts?