I own this app, along with Jing, Capto and SnapNDrag Pro. It's quite good, and getting better (although I'm a little leery of the upcoming cross-platform sync subscription that is apparently coming soon).
For me, the biggest miss is the feature that people seem to like the most: the immediate floating of the snapped image. I tend to use screenshot apps to make images I can drag as files into emails or iMessage, and that means I have to close those floating screenshots every time! (If there's a way to turn it off please let me know.)
It's very convenient, and MUCH faster than Capto. But sometimes I just end up launching SnapNDrag Pro instead of using Snappy already in my menubar, just because I don't want to deal with closing those floating screenshots. Also, one nice advantage of SnapNDrag Pro is that when you drag out a screneshot to the finder/email/iMessage you can set the image to automatically downsize to 75%/50%/25% of the original, and even specify the size of an optional black border.
If I could get resize and optional non-screenshot-float I'd be using Snappy all the time, and I'd give it 5 stars.