I am currently creating new puzzles for the Zirkel update which hopefully will be ready very soon. For this I use my custom editor.
During early development I worked on puzzles without actually seeing their layout on screen. Instead, I sketched ideas on paper and manually translated the ring coordinates and other properties to a nested text list which the game app would read. Only then could I see if there were any mistakes (or if it worked at all). As you can imagine this was a very tedious process and I pretty soon was longing for the comfort of a visual editor. So I made one.
As soon as I had this tool, things got much easier. I lay out the puzzle in the editor and create a file which can be read by my game. From an idea to testing it takes only a few minutes (of course creating good puzzles takes longer) and iteration is easy. Which is probably even more important is the ability to „think visually“ while creating a puzzle. When I was translating puzzles manually by entering values into a list all my brain could handle at that time was not to forget those numbers. Not much room for creativity. With the editor I can focus on creating challenging layouts.
Also, when I want to try a new mechanic, most of the time it is relatively simple to implement in the editor and the game and I can play around with it quickly.
Before creating your own tools you should always ask yourself: Will this thing save me enough time to justify developing it? For the Zirkel level editor my answer is clear: a thousand times, yes!