On the down side, customization isn't very straightforward in some cases. Also, the repeating events functionality is a bit quirky.
All in all, however, this is an outstanding extension. Support through the forum is fantastic, and all of my questions have been answered quickly and thoroughly.
The issues I listed above are minor, and I expect they'll be resolved in future releases (development is active at the moment). Congrats to the developer for a great extension!