I was very disappointed when I found out that the confirmation dialog box only displays the "Display Name" and the "Email address" from the address book entry. It doesn't display the "Organization" (or similar) which was the whole reason that I wanted this addon - i.e. to show me the organisations that the recipients are affiliated with before sending an email.
In other words, it only shows what you can already see in the email itself.
This would be much better if there were options to control which address book fields were displayed in the confirmation dialog box.
My workaround is to always include the organisation name in the "Display name" in the address book entry so that it shows up in both the standard auto completion and in the confirmation dialog box.
The addon's auto-completion doesn't seem to work anywhere near as well as the standard auto completion but with the workaround mentioned above it probably doesn't matter.
This review is for a previous version of the add-on (1.8).