When I encountered this document on Eric Jackson's website over the Independence Day weekend, I initially glossed over it as "meh, just another 2-cent banknote illegal usage"... but then I paused, reflected, and started looking through my records and my collection for a similar example... and couldn't find one.
It's tied, which is nice; something you don't always find, but what's so special about it?
This is actually the first example I have ever seen of one of the grilled banknotes used illegally as a revenue (Scott #135). It's hard to see in the image, but the grill is located in the southeast quadrant of the stamp.
I own many illegal usage examples of the grilled 1869 pictorial issue, as well as the grilled definitives of 1867, and you can locate examples of both without too much difficulty. They cost more than usages of the nongrilled issues of 1861, but if you can afford them they are obtainable. Scarcity is not so much a barrier as cost, scarcer grill types and denominations notwithstanding.
I also have numerous examples of the later nongrilled banknotes used as revenue stamps. Those actually tend to be a step down in therms of scarcity and cost.
So why are the grilled banknotes not found used as revenue stamps when the postage stamps issued both before and after them are?