With the basic Joomla banner system, you can have one banner across many different modules. This is great if you sell banner space by size but in different locations on the site. But if you upgrade to Ad Agency, you have to create multiple versions of the same banner on the system and then apply each to the different module positions. For some of my banner programs I sell, this quadruples the number of banners that I have to handle in the back end. Quite frustrating.
If you don't have your banners set up like this, then you will love this product. Just something that irked me, and assumed it would have this functionality since the basic Joomla system had it.
Now specifically for Komento - I think it's a great extension. The free template is pretty clean and didn't need a ton of tinkering to make it look extremely sharp. The only concern I have is that there appears to be issues for large sites with lots of comments. But they assure me it will be addressed in the next version, and for the first time in my development life, I believe them without a doubt.