And this one shown here $170

The pressure sensing happens on the pen itself not the screen, so it sends this data along the relative angle to the iPad

This does make me wonder why not an eraser on the other end...

It also happens that Lithium Ion degrades with time using it or not, undercharge, overcharge (granted, the charging circuit won't allow these 2), or temperature variations.

So it could go well down to ~2 years before needing too frequent charging.

Also since it's a pen, it will fall a lot, this will also lower this value.

Probably the pen will last long enough but it's definitely a product made to be replaced along the iPad or something like this.