As other have pointed out in questions; when the assignee receives the assignment they can view/comment on the platform which requires them to sign up. First name last name email password. People don't want to do that. The link should be to an open dashboard without need for registration. This is the major buff I have with this app.

Also I find several UX problems. You can't add a project while adding an assignment. You can't add project custom fields before saving a project. Characters aren't properly escaped in assignment title. Custom fields are only text, there's nothing else (drop down, checkboxes). Attachments are not shown in the message itself, they just appear as they do in a normal email. I could not find a way to edit/format the e-mail sent differently (for instance I don't want to add managers). Finally the platform is only available in English.

Overall the idea is interesting but I don't see what the platform brings to my workflow. Using my normal email works just as well. Nifty (another appsumo deal) does the same and much, much more.