The supporter's version allows you to save the data for all your recipes, and it calculates your additions in hundredths of a gram as opposed to tenths. It's "worth it" in the sense that its creator put and still puts a lot of work into something we use every time we brew to make the best beer that we can.
I donated and got the supporters version, but for some strange reason Excel won't let me open it, says it's protected with a password, which per Martin is not true. But I am perfectly happy with the free version, and I just save copies for my recipes (Android version of Excel requires you to make a copy in order to edit anyway.)
Frankenbrew makes the REAL point: I don't need the features of the supporters version. I don't care that it's a dead file in my cloud storage. I really just wanted to make a donation as some return for the great benefit I get from the "free" version.