eInk DPI and LCD DPI aren't really directly equivalent in terms of readability.

And this is a specialized device that seems much more suited to the type of work it's designed for than an iPad is. The iPad doesn't even support a stylus (except for the big nub stylus, which is really more of a stylized finger replacement).

ipad is heavier, smaller, not useable in bright light and with poor battery life in comparison. In fact, where is no comparison.

The iPad Air is light enough - I use one all day. The smaller size of the iPad is an advantage for portability. The iPad battery is more than good enough for a full day of work, so the comparison is empty. The iPad is highly usable in all indoor conditions. Bright sunlight is a problem for it.

That's only one advantage the Sony device has that matters, and it's a niche one.

Comparing this to ipad is pointless. It's a paper replacepemt, not a computer replacement.

An iPad is a paper replacement too.