The best is the kindness of the friendly team and how well everything has been conceived. No coding needed, you just drag and drop and set up your desired parameters. This includes various kinds of randomizations, notifications, reports, and can reach quite subtle levels even for complicated studies ! There's also that cool mobile interface, documents manager, and a big list of additional functions. I still have to discover some of them ! The support is fast whenever needed.

Flexibility, quick to answer if questions, easy to use