Maxed out the purchase at 3 codes to fully try this App and here's the scoop....
TLDR: As what other recent reviewers have said, there are bugs that currently make this unusable.

PROS:
- Beautiful premade templates and a nice drag and drop editor that I actually prefer over Mailchimp's
- Lots of features compared to other LTD email software.
- You can "group" contact lists which is useful when managing multiple brands so your brand (group) can have different contact lists within it.

CONS:
- Email verification doesn't work (which is what makes this App currently unusable). To verify a sender email you enter the email address you want to send emails from and then get sent an activation link. Unfortunately, clicking the activation link results in an error page. Tested with multiple emails, domains, and web browsers. Sent a message to support but haven't heard back (there's no instant chat).
- This App is advertised as being able to handle "multiple brands" and while that is technically true since you can add multiple domains and senders, it doesn't actually have brand management. For instance there is no where to create branded templates - you just create a newsletter and can then duplicate it if you want to reuse that design. Same goes for Forms, Reports, and Landing Pages. This gets very convoluted for Agencies that manage email marketing for multiple brands.
- There's 1 user (you) with no way of adding sub-users (ex. employees or clients). Also, you take up a contact spot.
- This one is odd, but your profile settings page is acutally on a totally different sub-domain (my.useinbox.com) and there are NO links back to the main sub-domain (id.useinbox.com) so if you click "edit profile" you have to either click "back" in your browser or reopen the App in a new browser tab. This only happens with the Profile page and none of the other settings pages...
- Transactional emails and email verifications are NOT unlimited. With any of the plans (I have 3 codes) you get 1,000 transactional emails included and 100 email verifications. You also have to turn these on seperately within your account as they're considered different Apps.

Also, to answer questions that were being asked (unsure why it's not specified in the product listing) you get UNLIMITED email sends with all plans. The only limit is subscribers. However, keep in mind that this is because you are sending emails through YOUR DOMAIN. If you're unsure of the risks regarding that, Google it.

As an agency owner looking for a Mailchimp alternative, I will personally be refunding. However, if they fix their email verification issue then this could be a good alternative for individuals.