It's unfair of me, but I'm always turned off when I see a desktop app that works on multiple platforms. That irrationally soured my first impression, because I think it otherwise looks like a great tool.
However, based on the fact that this app has an "in-Chrome browser" demo mode available... I'm assuming that it's REALLY a web application, packaged up for desktop use (like the Atom text editor).
Personally, I think that the Atom route of "HTML/JavaScript on the desktop" is a poor choice in most cases (a Bootstrap designer tool might be the rare exception). Regardless, there are multiple cross-platform frameworks out there today that look and work just great. Being turned off by cross-plat support is really an outdated bias, I think.
If they wrote it in Java and in that way claim multiple platforms, I daresay it would be even worse, on all platforms.
If they used a tool that did the conversion for them, it would likely be a security and usability disaster, even though I need sources for that.
So a bias against a multi-platform tool is understandable.
The one exception is a Javascript tool, since things like Chromium have a LOT of effort put into them by companies with thousands of developers on payroll. However the number of tools that should run in such a environment is limitted.