Hello Bart,
Can you tell us which version you are recommending?
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I'm using the Pro version, so I can use the images commercially, and the batch processing capability can come in handy there as well. The GUI and controls are realtime, so you can interactively see what you are doing. You can try a version for free, with an output size limitation. There is no documentation yet to speak of, but everything is very intuitive, and there are some tool tips implemented.
Have you tried running it under Windows 7?
I am running it on Win 7 Ultimate 64-bit without a problem. Asingle installer installs the correct version for the OS (32 or 64bits). All cores of the CPU are kept busy to get good user interaction, and reduce the immense ("under the hood") processing to do it's magic. I believe he also uses, or intends to use, the GPU's. Loading files can take a bit of time because a lot of data is pushed around to prepare for the tonemapping which is realtime.
I have not needed real support sofar, but I've exchanged some emails with feature requests, comments about image artifacts in the early versions, and such, and Sebastian usually responded promptly. That doesn't mean everything gets implemented (I have a few wishes left from my original but shrinking list), but if it makes sense to implement and it fits his development cycles he'll listen.
The programming is very clever. It shows that he's a competent programmer and has a good feeling for GUIs. Simple example, zooming in with the scroll wheel keeps the mouse position in focus. It's the attention for small details like that (and there are more)that shows he's given everything a lot of thought.
Cheers,
Bart