I can't speak on the technical side of your post, but my boss just purchased the Ink and Slide for me for Christmas and I have used it some on my iPad 2. I say "some" because I haven't really had time to sit and dig in and go through all of the features, etc. I can say that it does do basic lines and circles. I hope that helps. This is using the Adobe Line app.
I also purchased an Ink & Slide for use with my iPad Air 2 and am very unhappy with the obvious compatibility issues. Will someone from Adobe please respond and let us know when these problems will be resolved?
Thank you for your reply. The issue is not with the iPad 2 but with the iPad Air 2.
To be fair to Adobe and Adonit, this is a problem nobody saw coming, because Apple doesn't feel it important to inform partners of significant upcoming changes in their products. Wacom is in the same boat with the Intuos pen. I felt particularly let down as I bought an iPad only because the new touch apps are on iOS. Air 2 being the most recent, that's what I bought, only to discover (at about the same time Adobe, Adonit and Wacom were discovering it) that none of the pressure-sensitive pens on the market will work correctly with Air 2. I'm certainly not pointing the finger at Adonit, far less Adobe. This is all down to Apple's failure to let developers know about these changes in advance.
The Adonit SDK is currently being worked on heavily. Some mitigation of the problems with the Air 2 has been achieved, apparently, but according to the Adonit blog (http://www.adonit.net/blog/archives/2015/01/05/ipad-air-2/) there is still a long way to go. It may be that a change in iOS will have to happen, too, because it's definitely an issue that affects even finger touch. Wacom's engineers are also hard at work trying to find a software-only solution to what is mostly a hardware problem: http://community.wacom.com/en/inspiration/blog/2014/november/bamboo-stylus-fineline-and-in tuos-creative-stylus-2-compati…
Obviously, as Adonit pushes out changes in their SDK, those changes have to be incorporated into the Adobe apps and then thoroughly tested. Since Adonit doesn't yet know when (or if -- the Wacom guys were pretty sure that any fix would require hardware changes) a complete software fix will be available, you can hardly expect Adobe to do so.