Overall I have had a great experience using Mailjet, and would highly recommend using this software for any small to medium company. However, i would be cautious about the privacy of your email list.
Overall, I have had a positive experience with Mailjet. Very easy to learn and use, and includes lots of great templates. I error messages are limited compared to other similar softwares I have used.
My only main concern is the privacy of data. I feel like its not very transparent in terms of what they do with or leverage the data after each campaign has ended.