Look I am no expert with the use of post processing software. But I have been in IT for decades. Back in the eighties, when software like it took a lot to develop, it was maybe worth it but since then it has become bloatware, they spend a fortune on advertorials (yes all those tutorials in the photomags are paid for by Adobe) and everyone pirates it. As a result CS5/6 are over $1000 in Aus. That low price sight is definitely suspicious and I doubt that it is legal, at best they are flogging the one year educational version.
Yes all the plug ins are enticing but what about PixInsight, its about $200, its cross platform, its written specifically with astro in mind.
I have always use Gimp, its good, has always done anything I needed, and I have a clear mind. Now that I am looking for specific astro software I think I would definitely be buying PixInsight after looking at their free trial, especial seeing that for the one license fee I can put it on all my computer platforms
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Roger