difference Between Appian and K2

From what I see, Appian is based on J2EE whereas K2 is built on top of the Microsoft platform. 

From my perspective, I would think K2's integration to the Microsoft tier would be a lot tighter as the native backend engine is MS based.

I also tend to get a bit skeptical of the ease of use when I can't fine much online videos demonstrating the designer tools. 

Here's the videos uploaded by appian.

http://www.youtube.com/user/appian

And here is the K2 videos.

http://www.k2.com/en/K2TV.aspx

I couldn't find a proper live demo of Appian's technical feature  whereas there is a ton of those on the K2TV site.

Just note that this is of course my personal opinion as I have worked with other BPM vendors as a SI before I worked for K2.