The vast amount of robust capabilities built into the software platform, always finding new ways of accomplishing tasks and eventually easier ways of doing them.
It has more of a Microsoft/tech geek feel to the GUI and application's use, rather than the Apple business model for ease-of-use right out of the box, that most non-profit volunteers/activists are accustomed to using for getting a task done quickly — the obvious metaphor to me the difference between the mechanic who wants to get under the hood of his new car and tweak and modify like a hot rod, compared to the average person who wants to drive a Honda off the lot, to get from A-to-B effortlessly and reliably without much thought because they have bigger jobs to do than figure out the mode of transporation, that the car is just a tool and you shouldn't have to take multiple mechanic classes to figure out how to drive it.
Albeit, Mailchimp is a different platform for smaller email tasks for small groups, yet their ease-of-use GUI model helps the lay person get done quickly and with less confusion. Our IT personnel love the Salsa platform which is all that really needs to be said, yet the people who have to use it on a daily basis compare it to a flight cockpit of endless switches and tabs. For a premiere email database platform that Salsa is, I'm still waiting for emails I send to be fully-responsive and readable on the smallest smartphone. Just not there yet. Mentioned that at the last Salsa training event in San Francisco last fall, which we were told is coming... Still love the software platform. Even though the FAQs leave you wanting and confused with laborious hoops to jump through for answers to problems that mostly don't seem to work, sending a ticket to Salsa gets a quick, friendly response, a great answer and usually a screen capture of what precisely to do in a succinct manner, which should populate the FAQ area instead and the answer model to use.
And one last thought, as with the SF training event mentioned here, and the last Salsa conference in Virginia, it was an obvious sea of Apple laptops and iPads across the board at all events, all tables. So, the clientele around DC and elsewhere, the core target demographic for your software that traveled to the conference, prefer out of-the-box, ease-of-use products to get the job done, quickly.