[parkher]

I don't remember having any freezes with T1 or T2.
But I don't read with the native Sony reader, and I don't allow Sony to index my books.
So perhaps that is the reason that my readers are perfectly stable.
And I have 32 GB cards in all of them. And they are pretty full too.
Although about 10 GB perhaps are used for multiple dictionaries.
But still, 10-20 GB of books too.

With Cool Reader I don't have any problems you have with shelves on Kobo readers:
I use my own nested folders, and Cool Reader has its own internal file manager.
Besides, it has its internal last read book list (a stack, really) - you can get into it with a single button press (or touch) and once inside, for example, you may choose to get directly to the folder of any book in that list. In case you want to open another book in the same series, or just a close enough book to navigate through folders to a book you want.
Shelves, similar to Kobo shelves, are also on T1/T2. Thanks to rupor, who improved them, there are even auto shelves: each folder gets its own shelf automatically - it is very handy if you use Sony reader.
But I don't. I am very happy with Cool Reader - and it fully supports T1/T2 buttons too.
And allows to remap them any way I like.

So yes, Aura has an awesome screen but it demands such sacrifices from the user compared to almost perfect T2.