The Leadwerks community almost makes buying this product necessary; it seems like something I would like to be part of...
But for myself as a professional software engineer - timeis what is important (damn over-time). In the days of high school and college you don't have much choice of utilizing free/cheap software. Now that penny bank isn't so tight, so paying that extra cash for a nice GUI or Networking layer is highly worthwhile.
While using third-party software is a possibility, the integration often generates more work and problems. If someone has worked out those issues (such as CEgui), then thats one step closer to ideal. But, if I find a solution that has CEgui (or another) integrated nicely with an editor, well I may very likely open my pocket book to take advantage of doing less work for myself.
I also fully believe in focusing on your core features - better to have a few that stand out then a bunch of mediocre capabilities. Products like Ogre take a stance on only being a rendering engine - thus focusing on what they do well. This product states that it is a game engine, so from my perspective those core features include networking and GUI - which seem to be a bit lackluster.
Don't get me wrong - the presentation of the product, marketed features (rendering, lighting, etc.), tools, and the community do make this a great product. The less time I have to invest on working on the engine and more on the application - the better.
Is the documentation of the API publicly available? I didn't come across it on the Wiki/Support pages.