I am pretty cheap (can only think of one time I gave a website money and it was $5) and I've only used firecalc a couple of times. I'm one year out from retirement and if I start using firecalc more I might want additional features if there are any.
So, it pretty much boils down whether or not you’re feeling the value or the need to support.
On the results page, look for "Link to this set of data" near the upper right. Save that link as a bookmark or something, and that saves your data - use that link to to get to that set of data. You could bookmark different data sets if you are playing with different scenarios. This feature is free.If you register, can you save your data ($, years, expenses, etc) or do you still have to enter it every time you go to the site?
The donation gives you some more 'what if' type scenarios to play with. For example you can set different spending for different years (eg years 1-5 are $x/year... year's 6, 8, and 10 are different...) I found that feature useful when I was modelling years after the kids moved out. (Spending actually increases, in my mind, when that happens because travel kicks up.)
I'm cheap, too. But since I got a lot of value out of the calculator, I tossed a small amount of $ towards it. But that was me... Your mileage may vary.
So registration doesn't get any extra features and you can't save your data. Got it!
So registration doesn't get any extra features and you can't save your data. Got it!