This is what I can tell you:
I have Astropad Standard. Bought it early. It’s great for lasso work and anything outside of drawing in Photoshop (it works, but not to my liking, as far as the pressure curve goes…oddly, it works better for drawing in Clip Studio Paint). I usually use it wirelessly.
I’ve used Astropad Studio intermittently; the pressure curve options (and options in general) are quite effective. I’d advise, if you plan on using it regularly, to buy an annual license (you pay over $60 more per year if you pay monthly, so you don’t want to be a sucker if you can afford not to be).
So, the good news is that both work as one would expect.
The bad news:
This only works for Mac (and, I predict, probably will only ever work for Mac, as they’d be talking up a Windows conversion if they actually had it in the works). Don’t get me wrong, it works with the Mac really, really well…but you have to spend a good chunk of change just to be able to use this with your already expensive iPad Pro. (If you’re spending $649 for the smallest iPad Pro, another $99 for the Pencil, plus the least expensive iMac, you’ve already spent over $1800, not including software or apps). If it did work reasonably well with Windows, you could cut the overall price down by at least $300 (more than that if you know how to build a system yourself).
As an aside, Adobe is releasing Photoshop (at least) for the iPad Pro, if not also Illustrator and other programs. Assuming the port is successful, many people may not need Astropad for a lot of what we users have been using it for over the last few years. On the other hand, it’s completely possible that Adobe does a bad porting job (especially considering their lackluster apps for iOS so far), and people end up preferring to use Astropad coupled with a Mac for the foreseeable future.
In closing, TL:DR statement: It works, I like how it works (in general), though I wish I had more pressure curve options in Astropad Standard. I don’t use Astropad Studio right now due to the cost, and the fact that Clip Studio Paint is fully ported to the iPad Pro.