The ease to use, ability for multiple users (myself included) to access simultaneously, the many options available to customize our own process. I also like how it's always updating new features as well as existing ones! It can be difficult to keep up with all of the updates. But not much we dislike about this tool so far. We've been using fast-estimate since 2013 but have had 2 upgrades - one more recent than others which was nice. It has made my job easier by keeping track of things I would otherwise forget or take notes during meetings/meeting calls.