tl;dr: awesome tool (yet not perfect) with really great capabilities and some unique behaviors that make it fully deserve 5 Tacos.

I was very intrigued when I saw some of Xembly's Xena's capabilities - specifically the ability to have the assistant reschedule meetings, copy it on Email Messages, etc - awesome features that you don't see with most other assistants.
I bought the Tier 3 license pretty much on the spot.
I've been using Xena for about a week now, and all I have to say is WOW.
After trying a good number of these types of assistants over the last year, here is why I think Xena is better:
1. Meeting summaries are great. This isn't necessarily unique, some meeting assistants are better at it than others, but most can do a decent job. These are good and I'm happy about that.
2. Interaction with Xena happens inside Google Calendar. I'll admit at first I thought it was a bit weird - but it's AWESOME to access all of your meeting summaries, recordings, notes, etc on the calendar, and not having to log into a different website to search them.
3. OK, here's the biggest one for me. With all of the meeting assistants that I've tried so far, the biggest miss for me was that while they can provide summaries and even to-dos, they are always just there in the meeting. Xena actually automatically creates Tasks from meetings, and (mostly) assigns them to the right person. You can then check them off or ask others for status. But the greatest thing is that you can look at all of your tasks across meetings in one place... I have so many meetings that it's impossible for me to go back to each meeting summary to check for my to-dos, and this simply solves it.
4. Interacting with Xena in Slack is awesome. I love how it proactively blocked time on my calendar since it noticed my calendar was packed and I may not have time to check slack and emails. It asked me questions proactively and didn't just wait for me ask it to do things.

Having said all that - is the tool perfect?
Of course not. It still has transcribing errors sometimes, and it creates tasks for things that aren't necessarily tasks (i.e. "if we wanted to do that, we'd have to reimplement the entire project from scratch" --> task created to 'Reimplement the entire project from scratch')

I also don't like that I need to use Google Forms to add users to my account...

But considering tools on AppSumo are always a little underbaked, this one is already doing awesome things for me and I can't wait to see where it will go from here!