I really like this slick (3,7 MB) and fast tool. Especially in comparison to these "monsters" like Capto (50,9 MB) or Voila. It's great to have a separate library for my screenshots.
What I don't like is that there are a lot of features missing, that macOS does have nowadays. To name a few: Smart folders, Tags, good search or batch rename.
The integrated annotation feature is easier to use than in Preview, but I can't zoom or combine two images like in Preview. Good idea: SnapNDrag let me choose, if I want to annotate in Preview. But be aware, you can't use Drag'n'Drop. The changes won't be visible in SnapNDrag. So editing with Pixelmator is only possible outside the library.
There are also some strange UI decision. The search isn't placed in the toolbar, even if there's enough room. And renaming a file is not in-place like in Finder most native Apps. That's not Mac-like. But all in all SnapNDrag is quite more Mac-like than many other Apps like Capto or Monosnap.
The core capture tools are outperformed buy most other tools and macOS itself. I have to remember two shortcuts for selection or window snapshots and I can't switch between them with the space bar. The only plus for the selection capture is, that I can finetune the selection with the cursor keys. But without a magnifier it's hard to get it right. And why does it the selection capture hide my dock? To be fair: SnapNDrag can also import snapshots taken with the macOS shortcuts automatically.
What I really like is the group by date feature in the the thumbnail view (why only there?). I can collapse and hide old images with a click. To make a screenshot float is also very helpful in some situations.
SnapNDrag is a well thought tool, but with much room for enhancements. In my case it cannot replace every screenshot tool, but with the new import feature I can tie things together.