I bought the Aura HD pretty much the week it was released and have been very pleased with it. With one very important (to me) exception. The hightlighting worked very, very lously... I almost bought a Kindle just to be able to do highlights in the non-fiction books I read.
It got better maybe 1-2 years ago, but still very bad.
Now, I just realized I am half way through a book and have made many hightlights. All. Worked. Perfectly! Not one single problem.
No idea which firmware did the big change, but as of now, I'm very happy!
(For info, I use kepubs, tried epubs several times, sometimes it worked a bit better, but not good enough. And yes, I have reported it to Kobo (no pleasant experience).)