Quick heads-up: Filter Forge is now 70% off! I have been wanting to get a license, but the price of the pro version always seemed a bit steep to me. Just got a license myself. Full 16/32bit textures with all the texture channels required for materials, and no resolution limitations.
(and it works in Photoline - sorry, could not resist 
I looked at the filter gallery and I noticed that all the textures are square.
Does that indicate Filter Forge not having the ability to generate rectangular textures, because that might be a dealbreaker for a number of people. I looked to see if it had the ability when I found out the competing Genetica software is also limited to square textures (something which looks to currently be the exclusive domain of the Allegorithmic family of software like Mapzone and substance designer.)
Depends on the type of texture, of course. If the host app’s document size is 2500*1000 it will render the chosen texture in that (non-square) resolution. Of course, some textures are not suitable to render at arbitrary aspect ratios, and seamless tiling textures must be in square format, I believe.
I thought that last bit would be a limitation, but seeing Filter Forge can render to any size the square format for seamless tiles is not really an issue. Besides, creating a seamless texture in an image editor is a trivial job most of the time.
Btw, been playing all afternoon and it is very addictive. Some textures are quite amazing, and the node-based editor is simple to understand when you have Blender node experience.
Just checked, some textures also work with seamless tiling in rectangular format - again, it depends on the type of texture. Good to know.
All these deals and not enough time to use them. 
Damned Mayans.