I just purchased it.
For what it’s worth, I have the following on my editing PC and have used them all or am learning them:
Photoshop CC (been using Photoshop since at least 2004)
StarTools (started using last year)
PixInsight (started using yesterday!
SiriL (used for about a month or two)
Photoshop is, IMO, the easiest to come to grips with. Not because I’ve been using it for years but the interface follows more common conventions in software design. For example, with PixInsight, you will be confronted with sub windows in their corners that have triangles, squares, circles, ticks and crosses. Some of them you click, others you drag onto your image. Which one do you select? Why? It’s not straight forward at all. It will take learning before their way of doing things makes sense (have a look at an early Dylan Odonnel tutorial on PI to see what I mean. He says the same things I do… PI’s user interface is a mess)
StarTools is ridiculously powerful but I don’t find it flexible. Ivo’s very good software is great if you are a pure data scientist wishing to show an image that’s purely technically correct, but hard to understand if you like to push the boundaries.
There also isn’t much support on YouTube for the module and to this day I still don’t understand things like the Wipe Module fully
Siril is a great start if you want to go down the path of PI later as it’s similar in many ways but more basic in the UI (and IMO easier to understand). It follows similar workflows to PI. I quite like Siril
Creating star masks in PI and StarTools is a bit of a pain, probably more so in StarTools which I can never get right all of the time (sometimes it works, sometimes it doesn’t, even with manual editing)
That said, deconvolution is a lot easier in StarTools than PixInsight
A lot of this is more because I’m relatively new to Astro and the dedicated software is it what I’m used to. I have four pieces of software because I’m going to try them all.
What I would recommend at least is having PS installed. Even if you use Photoshop as the “finisher” for your workflow, it’s still very impressive.
Try out each of the others using this trial versions first to see which one you want. Siril is free so don’t worry about the trial for that.
Deep Sky Stacker is also more than enough to stack your images too. Not sure what the benefit is that PI provides with their solution, I haven’t seen a difference, it’s just more complex to execute
Take all of this with a grain of salt… just my $0.02