MailerLite first of all offers a unified experience for managing subscribers, their subscription options, email campaigns and automations. You do not need to jump through many hooks, everything can be managed via the same user interface. Also, it offers a good free tier forever (up to 1000 subscribers). Plus, it offers discounts for non-profit organizations. Review collected by and hosted on G2.com.
Have not found it easy to take a new subscriber's details from their submitted form in order to feed them into a follow-up webpage (e.g., to complete an order). Review collected by and hosted on G2.com.
