Well, here is a point of confusion. I think Demo (as always) posted an excellent response.
You said "In order to get the 6.0 upgrade ...". This sounds like a key point.
There are two apps that we seem to be discussing. Textilus - the basic product - sells for US$5.99. But, it is still at version 5.5.5! And this version was just posted two days ago.
There is another app, called Textilus Pro, which sells for US$9.99. Its version is currently 6.1, which was posted three days ago.
So I suspect you are talking about buying the Textilus to Textilus Pro Upgrade Bundle, which sells for US$11.99, and gives you the latest versions of both products.
Do you need Textilus Pro? Check it out before acting.