I've recently replaced my 505 with a T2.
It's a 6-inch dedicated e-ink reader with a SD card slot, and it has page change buttons. For everything else (change book, access TOC, use the dictionary, make bookmarks, change font, etc.) you have to use the touch screen.
Battery life is similar to that of the 505. It doesn't come with a cover, but there was an offer of cover plus wall charger from Sony at something around $38.
It has wi-fi and internet browser, which I found completely useless.
The screen is great (better than the 505's, which was already very good). Battery replacement is probably as difficult as with the 505.
What you win with the T2:
- Enhanced screen
- Large internal memory
- Selectable fonts
- More font sizes, smaller and bigger than base font
- Dictionary support
What you lose:
- Audio playback
- Support for LRF/LRX
While the 505 had a nice, high quality aluminium case, the T2 is plastic (which makes it much lighter). This may be an advantage or a disadvantage, depending on your preferences.
Personally, I am enjoying my T2 and don't miss my 505 (which is still in good working condition) at all.
Hope this helps.