It boggles my mind why anyone would use MailChimp. The most important trait for a good organization is ethics. When they acquired Mandrill, they did the same to PAYING customers[1]. They even turned off comments on the blog post of the announcement. And ever since they did these shady things, they super-charged their SEO to hide any mention of this fiasco. If you do a quick Google search for "mailchimp mandrill" you would no longer see the slew of articles of rants of paying customers like you used to. Really, the worst ethics I've seen in any internet company.

I stopped using MailChimp ever since and even though their integration is much simpler, I do not use them for my clients. Every now and then I do have one or two clients wanting to integrate with them, but I do honestly warn them of what they're capable of and be the judge.

It's not like they're cheap. Their plans are pricey and yeah, they do have good deliverability, but the competition has caught up ever since. The only way they're able to keep existing accounts is by passive-aggressive scare "Watchout, we have the best deliverability and if you move elsewhere for price concerns, you have tons of these problems to deal with, including deliverability, so stick with us".

This is 2018. No one should be using MailChimp. There isn't any good reason to.

[1] http://www.dangrossman.info/2016/02/28/mandrills-betrayal/